Hey everyone thanks for the advise. unfortunately i'm not allowed to use such functions. so i wrote this code, which works great with 1 problem. if i enter lets say 'hhjk' it will freak out. i want to clear the buffer after the first 'h' is detected as non-digit.. heard about the function fflush but i can't get to understand it..
int get_int()
{
char inp; /*inp, for input*/
int number; /*the same input but as integer*/
int flag=0; /*indicates if i need to ask for new input*/
do {
flag=0; /*indicates if i need to ask for new input*/
scanf("%c",&inp);
if (inp<48 || inp>57 ) /*this means it is not a number*/
{
inp=getchar(); /*Here i clear the buffer, the stdin for new input*/
printf("Try again...\n");
flag=1;
}
else
if (inp>53 && inp<58 && flag!=1) /*this means it is a number but not in the 0-5 range*/
{
inp=getchar(); /*here i clear the buffer, the stdin so i can get a new input*/
flag=1;
}
} while (flag);
number=inp-48; /*takes the ascii value of char and make it an integer*/
return number;
}
A simple way is to input a string, then check to make sure everything in there is a character. We can use strtol() to check since it returns a 0 when it can't do the converstion, the only condition is since you want 0 to be valid input, we have to put a special condition on the check:
int main()
{
char input[50]; // We'll input as a character to get anything the user types
long int i = 0;
do{
scanf("%s", input); // Get input as a string
i = strtol(input, NULL, 10); // Convert to int
if (i == 0 && input[0] != '0') { // if it's 0 either it was a numberic 0 or
printf("Non-numeric\n"); // it was not a number
i = -1; // stop from breaking out of while()
}
else if(i<0 || i > 5)
printf("wrong\n");
}while (i < 0 || i >5);
return 0;
}
Another way is to use the seldom seen %[] format for the scanf family. In the code below, I have %[0-9]. This gives us only numbers. ( haven't shown the return code, etc.)
do {
if ((scanf("%[0-9]%c", input, &nl) == 2) && (nl == '\n')) {
value = strtol(input, NULL, 0);
} else {
value = -1;
}
} while ((0 <= value) && (value <= 5));
Related
First, I apologize if the question doesn't make sense as my English isn't that good...
My question is, how do we print out different things depending on the user input?
What I'm trying to do is: when user inputs integer, the program prints out the inputted number. When the user inputs something that's not integer (like symbols and characters), the program prints out "not integer".
my current idea (pseudo-code) is as follows:
`int main(){
int value;
printf("Enter numbers");
scanf("%d", &value);
if(value is integer){
printf("%d", value);
} else {
printf("not integer");
}
return 0;
}`
what gets me is the scanf; by using %d, I'm assuming that the user will input an integer values, but the user can input values that are not integers so I can't make a comparison using the if statement if( value is integer). How can I make a comparison that will determine whether the inputted value is integer or not?
I don't know if this is a good thing or not.
You can use ASCII to check if the input type is an integer or not
(between 48 - 57 in ASCII)
it will be like this
char value;
int flag = 0; //to check true or false (0 means false, and 1 means true)
printf("Enter numbers");
scanf("%c", &value);
for(int i = 48; i <= 57; i++){
if(value == i){
flag = 1;
break;
}
}
if(flag == 1){
printf("%c", value);
} else {
printf("not integer");
}
How do you print different things depending the user input?
Step 1: Read the line of user input
char buf[100];
if (fget(buf, sizeof buf, stdin)) {
// something was entered
Step 2: test the string
char *end;
long value = strtol(buf, *end);
// If the end is the same as the beginning, no conversion occurred.
if (end == buf) {
puts("not integer");
}
printf("%ld\n", value);
}
}
Additional code could look for input that occurred after the integer. Also code could test for a large number that overflowed the long range.
The code is as follows. It caters for different situations like inputting negative numbers and decimal numbers:
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int main() {
char input[20];
int wrongFlag = 0;
scanf("%s", input);
if (input[0] == '0' && strlen(input) > 1) {
wrongFlag = 1;
//for number starts with 0, and string length>1 eg: 010
}
for (int i = 0; i < strlen(input); i++) {
if (i == 0 && (input[i] == '-' && strlen(input) > 2 && input[i + 1] == '0')) {
//check first round only: negative number with length >2 and starts with 0 eg: -010.
wrongFlag = 1;
continue;
}
if (i != 0 && !isdigit(input[i])) {
//check following rounds, check if it is not digit
wrongFlag = 1;
break;
}
}
if (wrongFlag) {
printf("Not integer");
}
else {
printf("integer");
}
return 0;
}
Try this it works for me.
#include<stdio.h>
#include<string.h>
int main()
{
int i;
char value[50];
int len;
printf("Enter maximum 50 digits\n");
/* enter the values you wanted*/
printf("Enter the value: ");
gets(value);
len = strlen(value);
/*it will iterate upto the end of the user input*/
for(i=0;i<len;i++)
{
if(48<value[i] && value[i]<=57)
{
if(i==(len-1))
printf("It's an integer");
}
else{
printf(" Not an integer");
break;
}
}
return 0;
}
I got up to here, but I still need to use while loop somehow. "want to play again(y/n)" and "Illegal guess. Your guess must be between 1 and 200.Try again. Your guess?" don't seem to work. Please help me with the while/do-while loop and fix my two problems above. Thank you.
#include <stdio.h>
int main()
{
int i,number,guess,tries=5,answer;
printf("Welcome to the game of Guess It!\nI will choose a number between 1 and 200.");
printf("\nYou will try to guess that number.If you guess wrong, I will tell you if you guessed too high or too low.");
printf("\nYou have 5 tries to get the number.\n\nOK, I am thinking of a number. Try to guess it.");
srand(time(NULL));
number = rand() % 200 + 1;
for (i=0;i<tries;i++) {
printf("\n\nYour guess? ");
scanf("%i",&guess);
if (guess==number) {
printf("**** CORRECT ****\n\nWant to play again(y/n) ");
scanf("%i",&answer);
if (answer=='y') {
return (i=0);
}
else (answer=='n'); {
printf("Goodbye, It was fun. Play again soon.");
}
}
else if (guess>number) {
printf("Too high!");
}
else if (guess<number) {
printf("Too low!");
}
else (guess>200); {
printf("Illegal guess. Your guess must be between 1 and 200.\nTry again. Your guess?");
}
}
printf("\n\nSorry, you ran out of tries.\n\nWant to play again?(y/n) ");
scanf("%i",&answer);
if (answer=='y') {
return (i=0);
}
else if (answer=='n'); {
printf("Goodbye, It was fun. Play again soon.");
}
return 0;
}
First, and most important, turn on warnings. You have several elementary mistakes in your code that would be caught with compiler warnings. They're unfortunately off by default. -Wall turns on the basic warnings. It's not "all" warnings, because this is C! -fsanitize=address -Wall -Wshadow -Wwrite-strings -Wextra -Wconversion -std=c99 -pedantic is a good set of warnings to work with.
You could put a loop around the loop, but that rapidly gets hard to maintain. Instead, put the game into a function and loop around that.
void do_game(int tries) {
int number = rand() % 200 + 1;
for (int i=0; i < tries; i++) {
int guess;
printf("\n\nYour guess? ");
scanf("%i",&guess);
if (guess == number) {
printf("**** CORRECT ****\n\n");
return;
}
else if (guess > number) {
printf("Too high!");
}
else if (guess < number) {
printf("Too low!");
}
else if (guess > 200) {
printf("Illegal guess. Your guess must be between 1 and 200.\nTry again. Your guess?");
}
}
puts("\n\nSorry, you ran out of tries.\n\n");
return;
}
Note how the game only has to concern itself with the game. No other logic or questions about playing another game. And it can immediately return when the game is over.
Then the rest of the program is pretty simple. Run the game in an infinite loop, break out of it when you're done.
int main() {
printf("Welcome to the game of Guess It!\nI will choose a number between 1 and 200.");
printf("\nYou will try to guess that number.If you guess wrong, I will tell you if you guessed too high or too low.");
printf("\nYou have 5 tries to get the number.\n\nOK, I am thinking of a number. Try to guess it.");
srand(time(NULL));
while(1) {
do_game(5);
char answer;
printf("Want to play again?(y/n) ");
scanf("%c",&answer);
if (answer == 'n') {
printf("Goodbye, It was fun. Play again soon.");
break;
}
}
return 0;
}
There's a problem, and it's scanf. It's always scanf. scanf is such a problem, there's a whole FAQ for it.
scanf("%i") reads a single integer but not the following newline. That newline, and any other extra input, hangs around on stdin. A later scanf("%c", &answer); might then read that newline instead of their answer.
scanf("%i\n") does not solve the problem. That tells scanf to read an integer, then a newline, then look for another non-whitespace character. scanf is weird.
You're much better off reading the whole line with fgets and parsing it with sscanf. You can write a little utility function for that which gets into variadic arguments.
void line_scanf( const char *fmt, ... ) {
// Get the list of arguments.
va_list args;
va_start(args, fmt);
// Read a line.
char line[256];
fgets(line, sizeof(line), stdin);
// Scan the line like sscanf() but with a va_list.
vsscanf( line, fmt, args );
// Close the list of arguments.
va_end(args);
}
Then use it just like scanf. It guarantees to read the whole line and not leave newlines or partial input on the buffer.
int guess;
printf("\n\nYour guess? ");
line_scanf("%i",&guess);
This is only a partial answer, but it can be a starting point. You really should have a reliable input function. Your scanf() won't do, even if you fix the obvious errors trying to get a character using %i, which is for integers. I won't go into details here, I wrote a document on this. (Basically, you will at least run into problems with unparsable input that scanf() will just leave unread.)
Here's an example how you could do reliable input for your usecase with comments along the way:
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define INVALIDNUMBER -1
#define READERROR -2
int readPositiveNumber(void)
{
char buf[64];
// read a line:
if (!fgets(buf, 64, stdin)) return READERROR;
size_t len = strlen(buf);
// line was empty -> invalid:
if (!len) return INVALIDNUMBER;
// line was not complete (last character isn't newline):
if (buf[len-1] != '\n')
{
// read the rest of the line
do
{
if (!fgets(buf, 64, stdin)) return READERROR;
} while (!buf[strcspn(buf, "\n")]);
// input was invalid
return INVALIDNUMBER;
}
// convert to number:
char *endptr;
long num = strtol(buf, &endptr, 10);
// endptr == buf means no characters could be parsed as a number,
// endptr doesn't point to newline means there were non-numeric characters later:
if (endptr == buf || *endptr != '\n') return INVALIDNUMBER;
// if result is out of range of int or is negative -> invalid:
if (num > INT_MAX || num < 0) return INVALIDNUMBER;
return (int)num;
}
int main(void)
{
fputs("Enter a number between 1 and 200: ", stdout);
int number = readPositiveNumber();
if (number == READERROR) return EXIT_FAILURE;
while (number < 1 || number > 200)
{
fputs("Enter a valid number between 1 and 200: ", stdout);
number = readPositiveNumber();
if (number == READERROR) return EXIT_FAILURE;
}
printf("You entered %d.\n", number);
return EXIT_SUCCESS;
}
Try to understand this function, read the manuals for functions you don't know or understand (google "man strtol" for example will find you a manual page for strtol()).
For reading your yes/no response, use fgets() as well, but of course this function will look different, like check if the input is only 1 character (the second one has to be '\n') and return this one character.
just because it's a bit of fun, here's a possible whole game working robustly:
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#define INVALIDINPUT -1
#define READERROR -2
static int readLine(char *buf, size_t bufsize)
{
if (!fgets(buf, bufsize, stdin)) return READERROR;
size_t len = strlen(buf);
if (!len) return INVALIDINPUT;
if (buf[len-1] != '\n')
{
do
{
if (!fgets(buf, bufsize, stdin)) return READERROR;
} while (!buf[strcspn(buf, "\n")]);
return INVALIDINPUT;
}
return 0;
}
static int readPositiveNumber(void)
{
char buf[64];
int rc = readLine(buf, 64);
if (rc < 0) return rc;
char *endptr;
long num = strtol(buf, &endptr, 10);
if (endptr == buf || *endptr != '\n') return INVALIDINPUT;
if (num > INT_MAX || num < 0) return INVALIDINPUT;
return (int)num;
}
static int readYesNo(void)
{
char buf[64];
int rc = readLine(buf, 64);
if (rc < 0) return rc;
if (buf[0] == 'y' || buf[0] == 'Y')
{
if (buf[1] == '\n') return 1;
if ((buf[1] == 'e' || buf[1] == 'E')
&& (buf[2] == 's' || buf[2] == 'S')
&& buf[3] == '\n') return 1;
return INVALIDINPUT;
}
if (buf[0] == 'n' || buf[0] == 'N')
{
if (buf[1] == '\n') return 0;
if ((buf[1] == 'o' || buf[1] == 'O')
&& buf[2] == '\n') return 0;
return INVALIDINPUT;
}
return INVALIDINPUT;
}
int main(void)
{
srand(time(0));
for (;;)
{
int number = rand() % 200 + 1;
int tries = 5;
int found = 0;
while (tries--)
{
int guess = INVALIDINPUT;
while (guess < 1 || guess > 200)
{
fputs("guess [1..200]: ", stdout);
guess = readPositiveNumber();
if (guess == READERROR) return EXIT_FAILURE;
}
if (guess == number)
{
puts("Correct!");
found = 1;
break;
}
else if (guess < number) puts ("Too low!");
else puts("Too high!");
}
if (!found)
{
puts("No luck!");
}
int yn = INVALIDINPUT;
while (yn < 0)
{
fputs("play again (y/n)? ", stdout);
yn = readYesNo();
if (yn == READERROR) return EXIT_FAILURE;
}
if (!yn)
{
puts("Bye!");
return EXIT_SUCCESS;
}
}
}
This exercise is an exercise to ingrain in your mind why scanf is generally a bad choice for taking mixed user input! You can do it, but you must be very careful to account for any characters that remain in the input buffer (i.e. stdin) -- especially when taking character input... Why?
When you enter a value that is read by scanf, the '\n' will always remain in the input buffer (unless accounted for in your format string). Further, on a failed conversion -- all characters will remain in the input buffer. Further, the user can do something stupid like entering "4 is my guess" when prompted leaving is my guess\n for you to deal with.
Further, what if the user cancels input by pressing ctrl + d (or ctrl + z on windoze) generating a manual EOF? You must account for all possibilities for each and every input.
You must also use the correct format specifier to read input. You are not going to read 'y' or 'n' with %d or %i. When you want to read an int use %d when you want to read a char, use %c. You must also take into account that %c never skips leading whitespace.
(you beginning to understand why it's better to use fgets and then call sscanf for user input??)
How do you handle the characters that remain in the input buffer? Well generally you will use getchar() to read until you have read '\n' (generated by pressing Enter) or until EOF is encountered. You can make it easy on yourself by writing a short function like the following:
/* empty characters that remain in stdin */
void fflushstdin ()
{
for (int c = getchar(); c != '\n' && c != EOF; c = getchar()) {}
}
If you call fflushstdin after each input, you will always take care of any characters that remain. If you know chars remain from a prior input that have not been removed, then call it before taking input.
Don't use magic numbers in your code (e.g. 1, 5, 200), instead define any needed constants at the beginning of your code and use the constants in your code. Why? If they change, then you have a single readily accessible place to change them and you don't have to go picking though your code to find them. You can use a #define or an enum like the following:
enum {LOW = 1, TRIES = 5, HIGH = 200 };
The remainder of your problems are simply logic problems that you can work out. Incorporating the above, you can handle (what I think you are attempting to do) as follows:
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
enum {LOW = 1, TRIES = 5, HIGH = 200 };
/* empty characters that remain in stdin */
void fflushstdin ()
{
for (int c = getchar(); c != '\n' && c != EOF; c = getchar()) {}
}
int main (void) {
int i, number, guess, ret;
char answer;
printf ("Welcome to the game of Guess It!\n"
"I will choose a number between %d and %d.\n"
"You will try to guess that number.\n"
"I will tell you if you guessed too high or too low.\n"
"You have %d tries to get the number.\n\n"
"OK, I am thinking of a number. Try to guess it.\n\n",
LOW, HIGH, TRIES);
srand(time(NULL));
while (1) { /* outer loop until user quits */
number = rand() % HIGH + 1; /* set number INSIDE loop */
for (i = 0; i< TRIES; i++) { /* loop for set number of TRIES */
while (1) { /* validate user guess, handle cancelation */
printf ("Your guess no. %d? ", i + 1); /* prompt */
if ((ret = scanf (" %d", &guess)) != 1) { /* chk return */
if (ret == EOF) { /* check for cancelation */
printf ("input canceled, exiting.\n");
return 0;
}
fprintf (stderr, " error: invalid input.\n");
fflushstdin(); /* empty chars remaining in stdin */
continue;
}
if (guess < LOW || guess > HIGH) /* check limits */
printf("Illegal guess. Your guess must be between "
"%d and %d.\nTry again. Your guess?", LOW, HIGH);
break;
}
if (guess == number) { /* correct answer */
printf ("\n**** CORRECT ****\n\nWant to play again(y/n) ");
fflushstdin();
/* validate answer, you are reading a `char` NOT `int` */
while ((ret = scanf (" %c", &answer)) != 1 ||
(answer != 'y' && answer != 'n')) {
fprintf (stderr, "error: invalid answer, play again (y/n) ");
if (ret == EOF) { /* check for cancelation */
printf ("input canceled, exiting.\n");
return 0;
}
fflushstdin(); /* empty chars remaining in stdin */
}
if (answer == 'y') /* use goto for breaking nested loops */
goto done;
printf ("Goodbye, It was fun. Play again soon.\n"); /* no */
return 0;
}
if (guess > number) /* provide > and < feedback */
printf ("Too high!\n");
if (guess < number)
printf("Too low!\n");
}
printf ("Sorry, you exhausted all your tries, number was: %d\n"
"play again (y/n) ", number);
fflushstdin();
/* validate answer, you are reading a `char` NOT `int` */
while ((ret = scanf (" %c", &answer)) != 1 ||
(answer != 'y' && answer != 'n')) {
fprintf (stderr, "error: invalid answer, play again (y/n) ");
if (ret == EOF) {
printf ("input canceled, exiting.\n");
return 0;
}
fflushstdin();
}
if (answer != 'y')
break;
done:; /* goto lable to play again after correct asnwer */
}
return 0;
}
Example Use/Output
$ ./bin/guess
Welcome to the game of Guess It!
I will choose a number between 1 and 200.
You will try to guess that number.
I will tell you if you guessed too high or too low.
You have 5 tries to get the number.
OK, I am thinking of a number. Try to guess it.
Your guess no. 1? onehundred
error: invalid input.
Your guess no. 1? 100
Too low!
Your guess no. 2? 150
Too high!
Your guess no. 3? 125
Too low!
Your guess no. 4? 137
Too high!
Your guess no. 5? 131
Too low!
Sorry, you exhausted all your tries, number was: 132
play again (y/n) y
Your guess no. 1? 100
Too low!
Your guess no. 2? 150
Too low!
Your guess no. 3? 175
Too low!
Your guess no. 4? 187
Too high!
Your guess no. 5? 181
**** CORRECT ****
Want to play again(y/n) y
Your guess no. 1? 100
Too low!
Your guess no. 2? 150
Too high!
Your guess no. 3? 125
Too high!
Your guess no. 4? 112
Too high!
Your guess no. 5? 106
Too low!
Sorry, you exhausted all your tries, number was: 110
play again (y/n) n
Note, the above handles stupid user input (like onehundred) and adds number to the failure output to let the user know what he missed.
Look things over and let me know if you have further questions.
scanf("%i", ...) reads integers in base 10, not characters or strings.
You need to organize your loops. You have 2 main loops, one that runs while the user wants to keep playing, and another that runs while the a game is on.
You program in a nutshell:
int main()
{
// loop until player has had enough
// pick a number
// game loop :
// get a number from user:
// user entry loop:
// print prompt
// get user entry
// validate
// loop number from user: until 0 <= entry <= 200
// if number is ok
// user has won, exit game loop
// if too low
// say 'low'
// if too high
// say high
// if # of attempts > MAX
// say 'lost' exit game loop
// end game loop
// want to contine?
// user entry loop:
// print prompt
// get user entry
// validate
// loop user entry loop until 0 <= entry <= 200
// end loop
}
You could start your loops within main a bit like this:
int attempts;
char yesno = 0;
int guess;
do // loop until player has had enough
{
// generate a number here
attempts = 0;
while(1) // loop while game is on
{
while (1) // loop until user entered a valid entry
{
// prompt
// get user guess
if (0 <= guess && guess <= 200)
break;
}
if (guessed right)
{
// game over!
break;
}
// tell if high or low.
if (++attempts <= MAX)
{
// game over!
break;
}
}
do // loop until user entered a valid entry.
{
printf("Another game (y/n)?");
yesno = fgetc();
} while(yesno != 'y' && yesno != 'n'); // could make case-insensitive ?
} while (yesno != 'n');
There are probably as many ways to do this as there are numbers between 0 and 200. A good strategy is to start by writing comments in your C file that describe step by step what the program needs to do. Going through them one by one is much easier than having the program only in your head, especially when you are starting to code. It will get easier with time as you get used to juggle the concepts and basic blocks your mind.
When I enter a letter the loop runs infinitely. Does a letter store as a zero when it is input as an int? How can I reject a non digit answer, just I have rejected an answer outside the range?
int main(int argc, const char * argv[]) {
// insert code here...
int categoryToScore;
int categoryScores = 6;
printf("Enter category to save score: ");
scanf("%d", &categoryToScore);
while (categoryToScore >= categoryScores || categoryToScore <= 0) {
printf("Error: invalid command. Enter 1-5 to save to an unused category\n");
printf("Enter category to save score: ");
scanf("%d", &categoryToScore);
}
return 0;
}
Just for background
I want to:
print a request an input that is between 1 and an upper bound
scanf for the input
check if the input is of a correct type and within the correct range
if it isn't then print an error message and go back to 1.
if it is then proceed
You are asking scanf to read a number from standard input. Scanf finds a non-digit character in the standard input and does not remove it from the standard input. Scanf fails and returns 0 (the number of fields successfully processed).
The next time you call scanf, it finds the same character at the start of standard input. So the process repeats indefinitely.
One solution is to read stdin one character at a time.
Another solution is to read (and discard) the one character from stdin before calling scanf again.
int main(int argc, const char * argv[]) {
// insert code here...
int categoryToScore;
int categoryScores = 6;
int scantRetVal;
printf("Enter category to save score: ");
scantRetVal = scanf("%d", &categoryToScore);
if (scantRetVal != 1) {
getchar(); // read and discard one character from stdin
categoryToScore = 0;
}
while (categoryToScore >= categoryScores || categoryToScore <= 0) {
printf("Error: invalid command. Enter 1-5 to save to an unused category\n");
printf("Enter category to save score: ");
scantRetVal = scanf("%d", &categoryToScore);
if (scantRetVal != 1) {
getchar(); // read and discard one character from stdin
categoryToScore = 0;
}
}
return 0;
}
Rather than fix this particular program I will show how to solve ANY similar problem using a concept called an "exit condition".
The idea of an exit condition is that you have an infinite loop and it has various exit conditions. Often there are two exit conditions: one for success and one for an error.
while( true ){ /* infinite loop */
char c = ... /* get the character you want */
if( c < '0' || c > '9' ){
printf( "invalid character, not a digit\n" );
continue; // get another character
}
... /* do whatever you with valid data */
if( c == '3' ) break; /* your exit condition, whatever it is */
if( c == '7' ) exit(0); /* exit the whole program */
}
Note: If you are accepting free form input (numbers and strings), scanf is probably not a good idea. scanf accepts very specific, well-formatted input. So if you ask for a %d, then there better be a %d (decimal number) in the input or you will have problems.
For example, if you accept numbers and strings, you should take everything as strings using fgets or something like that.
Here is a complete program that does what you want:
#include <stdio.h>
#include <stdbool.h>
int main(int argc, const char * argv[]) {
int iMaxScore = 6;
int charInput = 0;
int iInputValue = 0;
while( true ){
printf("Enter category to save score: ");
GetInput:
charInput = getchar();
if( charInput == 10 || charInput == 13 ) goto GetInput; /* ignore enter key */
if( charInput == 'q' ) break;
if( charInput < '0' || charInput > '9' ){
printf( "invalid entry, not a digit %d\n", charInput );
break;
}
iInputValue = charInput - '0';
if( iInputValue > iMaxScore ){
printf( "Error, input value exceeds maximum category %d\n", iMaxScore );
continue; /* try again */
}
printf( "you entered category %d\n", iInputValue );
/* continue ... */
}
return 0;
}
Can someone help me to solve my problem? I have a problem with %[^\n]. When I try to enter a false input the program loop the warning that I wrote, but if I use %s and I enter my string the next statement is not working properly.
#pragma warning (disable:4996)
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int main(){
char name[30];
char number[12];
int flag, flag1, flag2, flag3;
int i;
printf("Add New Contact\n");
do {
printf("input name [1..30 char]: ");
scanf("%[^\n]", name); fflush(stdin);
if ((name[0] >= 'A' && name[0] <= 'Z') || (name[0] >= 'a' && name[0] <= 'z')) {
flag = 1;
}
else {
flag = 0;
printf("First letter of name should be an alphabet (A-Z or a-z)\n");
}
if (strlen(name) > 30) {
flag1 = 0;
printf("Length of name should be between 1 and 30 characters\n");
}
else {
flag1 = 1;
}
} while (flag == 0 || flag1 == 0);
do {
printf("Input phone number[6..12 digits]: ");
scanf("%s", number); fflush(stdin);
for (i = 0; i < strlen(number); i++) {
if (number[i] >= '0' && number[i] <= '9') {
flag2 = 1;
}
else {
flag2 = 0;
}
}
if (flag2 == 0) {
printf("Phone numbers should only contain digits (0-9)\n");
}
if (strlen(number) >= 6 && strlen(number) <= 12) {
flag3 = 1;
}
else {
flag3 = 0;
printf("Length of phone numbers should be between 6 and 12 digits\n");
}
} while (flag2 == 0 || flag3 == 0);
printf("\n");
printf("New contact successfully added!\n");
printf("Press Enter to continue...");
getchar();
getchar();
return 0;
}
Oh by the way, the problem might simply be that the scanf call leaves the newline in the buffer, and if you loop and try again the first character seen will be the newline and scanf should not read any thing.
There are two things you should do: First check what scanf returns, it should return 1 if it read a string. Secondly you should tell scanf to discard any possible leading white-space by adding a space first in the format string: " %[^\n]".
Most scanf formats automatically skips leading white-space, but not when using the "%[" or "%c" formats.
Also, to not worry about writing out of bounds of the array, you should add a length modifier to make sure that scanf doesn't read more input than it can write: " %29[^\n]". If the length of the string is 29 after this, then you should probably read until you reach the end of the line, character by character.
Here is your program fixed:
#include <stdio.h>
#include <ctype.h>
#include <string.h>
// In case you need this -- not needed for this case
void discard_input()
{
char c;
while( ( c = getchar() ) != '\n' && c != EOF );
}
void remove_trailing_newline(char * s)
{
char * ch = s + strlen( s ) - 1;
while( ch != s ) {
if ( *ch == '\n' ) {
*ch = 0;
break;
}
--ch;
}
return;
}
int main(){
char name[30];
char number[12];
int flag, flag1, flag2, flag3;
int i;
printf("Add New Contact\n");
do {
printf("\nInput name [1..30 char]: ");
fgets( name, 30, stdin );
remove_trailing_newline( name );
flag1 = flag = 1;
if ( !isalpha( name[ 0 ] ) ) {
flag = 0;
printf("First letter of name should be an alphabet (A-Z or a-z), found: %s\n", name );
}
// impossible
if (strlen(name) > 30) {
flag1 = 0;
printf("Length of name should be between 1 and 30 characters\n");
}
} while (flag == 0 || flag1 == 0);
do {
printf("\nInput phone number[6..12 digits]: ");
fgets( number, 12, stdin );
remove_trailing_newline( number );
flag2 = flag3 = 1;
int len_phone = strlen( number );
for (i = 0; i < strlen(number); i++) {
if ( !isdigit( number[ i ] ) ) {
flag2 = 0;
}
}
if (flag2 == 0) {
printf("Phone numbers should only contain digits (0-9), found:'%s'\n", number);
}
if ( len_phone < 6 || len_phone > 12) {
flag3 = 0;
printf("Length of phone numbers should be between 6 and 12 digits, found: %d\n", len_phone );
}
} while (flag2 == 0 || flag3 == 0);
printf("\n");
printf( "Name: '%s'\n", name );
printf( "Phone: '%s'\n", number );
printf("New contact successfully added!\n");
printf("Press Enter to continue...");
getchar();
return 0;
}
You can find the program here.
The fixings are more or less interesting, I enumerate they here:
At first, I thought that the problem was that the trailing new line was being left in the input buffer. fflush(stdin) is actually undefined behaviour in C, since the fflush() function is there for output streams. Anyway, I included the code in question 12.26b of the comp.lang.c FAQ, since I think it is interesing to have it as reference. Then, I decided to change scanf() with fgets(). This is due to the scanf() taking spaces as delimiters, so you wouldn't be able to write a complete name, i.e., name and surname. Remember that gets() is not an option, since it writes the input past the limit of the buffer. Actually, fgets() solves this by letting us define a limit of chars to read. The problem is that fgets() also includes the '\n' in the buffer, so, that's why I included the remove_trailing_newline() function. Tricky, isn't it?
You added a condition to check whether the name input had more than thirty chars. Actually, this is impossible to check in your program. First of all, fgets() will read 29 chars + the final char mark (0). Secondly, if you were actually allowing to input more than 30 chars, then the input would be written past the size of the buffer, which is undefined behaviour (crashes in most cases). You would have to use something more complex, like std::string in C++, and then check its length. Or maybe use a third party expandable string for C. Or roll out your own expandable string...
You can decide whether there is an alphabetic char or a digit by using isalpha(c) and isdigit(c) functions.
When you are going to use a value many times, such as strlen(name), then you should precompute it and store it in a local variable. Though a good compiler (its optimizer) will detect this situation and solve it for you, you never know which compiler is going to compile your code, and how advanced it is. Also, there is nothing wrong making things easier for the optimizer.
When you have a situation in which you set a flag for signaling an error condition, it is easier to set it to the "no error" value before checking anything, and solely in case of an error, set it to the "error" value. This will be easier to read, and therefore, to understand.
Hope this helps.
I've searched in and out of these forums but am still having trouble. My understanding of C is still very basic. I'm creating a small program that takes 3 numerical values entered by the user and then calculates the highest. I nailed that.
I now want to ensure that the user enters only integer values. I managed to get the prog to keep prompting the user to re-enter the value until it is within the specified numerical range (for example, any number between 1 and 1000 inclusive, piece of cake) but that's not good enough. I used 3 while loops to test each value, but this only works as long as the input is of type integer.
The trick is I cant use built in functions. It needs to be manual (sorry, poor choice of words) I tried to use char variables and x = getchar(); to get the ASCII value and test it in a condition but I can't get it working in a loop. (while/ do-while)
I also tried using a "for loop" and array variables but once again am struggling to get it to keep prompting the user.
I've also tried to test the value returned by scanf to see if its integer but my knowledge level of correct C syntax is level: noob. Either my loops don't loop or they loop infinitely.
Here is some sample code:
int x, y, z =0;
printf("Enter the first number:\n");
scanf("d", &x);
while (condition) /* Here is where I need to determine that the entered val is false */
{
printf("Wrong input. Re-enter a valid value.\n");
x =0;
scanf("%d", &x); /*user re-prompted */
}
I'm getting the idea that I'll have to use ASCII and a loop, but I just can't get to it. Also, the values entered get sent to a function for comparing and are then returned.
Could someone give me some advice and a few tips please?
Much thanks
You would have to use something like fgets, and strtol:
long someValue;
char *bufEnd = NULL;
char buf[128]; // max line size
do {
printf("enter a value: ");
fgets(buf, 128, stdin);
someValue = strtol(buf, &bufEnd, 10); // base 10
} while (bufEnd == buf || *bufEnd != '\n');
printf("got value: %li", someValue);
What we are doing here is we are tapping into strtol's capability to tell us where it stopped parsing, by passing in bufEnd.
Then, we are making sure that bufEnd doesn't point to the beginning of buf (in which case, it didn't start with a number), and also checking to make sure that bufEnd points to \n, or the end of the line (making sure that the user didn't enter something like 123abc, which strtol would interpret as 123). You may wish to trim buf of whitespace characters first, however.
You're absolutely on the right track with "scanf()". Just check the return value. If you don't get the expected #/values, then you got invalid input:
char found = FALSE;
int ival;
double x;
while (!found)
{
printf("Please enter a valid integer: ");
if (scanf("%d", &ival) !=1) {
printf ("Invalid! Please re-enter!\n");
continue;
}
printf("Please enter a valid floating point number: ");
if (scanf("%lf", &x) !=1) {
printf ("Invalid! Please re-enter!\n");
continue;
}
found = TRUE;
}
Here's my solution. It safe against buffer overflow and straightforward .
#include <stdio.h>
#define LEN 10
int main() {
int a;
char str[LEN];
fgets( str, LEN, stdin );
while ( !sscanf( str, "%d", &a ) )
fgets( str, 10, stdin );
printf("Num is : %d\n", a);
return 0;
}
#include <stdio.h>
#include <limits.h>
#include <ctype.h>
int getInteger(int* err){
int ch;
int n;//int32
int takeNum, sign;
long long int wk;//long long int as int64
wk=0LL;
*err = 0;
takeNum = 0;//flag
sign = 1;//minus:-1, other:1
/* //skip space character
while(EOF!=(ch=getchar()) && (ch == ' ' || ch == '\t' || ch == '\n'));
ungetc(ch, stdin);
*/
while(EOF!=(ch=getchar())){
if(ch == '-'){
if(takeNum != 0){//in input number
*err = 1;
break;
}
if(sign == -1){//already sign
*err = 2;
break;
}
sign = -1;
continue;
}
if(ch >= '0' && ch <= '9'){//isdigit(ch) in ctype.h
if(takeNum == 0)
takeNum = 1;
wk = wk * 10 + (ch - '0')*sign;
if(INT_MAX < wk || INT_MIN > wk){//overflow
*err = 3;
break;
}
continue;
}
if(ch != '\n'){//input other [-0-9]
*err = 4;
}
break;
}
if(takeNum == 0){//not input number
*err = 5;
} else {
n=wk;
}
while(ch != '\n' && EOF!=(ch=getchar()));//skip to newline
return n;
}
int getValue(const char* redoprompt, int low, int high){
int num, err=0;
while(1){
num = getInteger(&err);
if(err || low > num || high < num)
printf("%s", redoprompt);
else
break;
}
return num;
}
#define max(x,y) ((x)>(y))? (x) : (y)
int main(){
const char *error_message = "Wrong input. Re-enter a valid value.\n";
int x, y, z, max;
x = getValue(error_message, 1, 1000);
y = getValue(error_message, 1, 1000);
z = getValue(error_message, 1, 1000);
max = max(max(x,y), z);
printf("max:%d\n", max);
return 0;
}