I'm error checking for letters. If a letter is entered then its suppose to print out error and exit. If its a number then it's suppose to run the statement (which I didn't put in the code since its irrelevant at the moment) under the if. When I enter a number it should run the if statement but when I enter a letter or a number it goes to the else statement.
#include <stdio.h>
#include <ctype.h>
int main()
{
int x;
printf("Enter up to 10 positive integer ending with EOF:\n");
while((scanf("%d",&x)) != EOF && x < 100){
if( isdigit(x) ){
//statement
}
else{
printf("error, wrong input\n");
return 0;
}
}
if(x >= 100)
printf("error, wrong input\n");
return 0;
}
You want isdigit to check a char , please change scanf to :
while((scanf("%c",&x)) != EOF && x < 100){ // yes x is an int, but here you want a char
Related
I want to strictly limit a user's input on an integer in this program to 2-12 only. How do I do that?
#include <stdio.h>
int main(){
int i;
scanf("%d", &i);
int diceThrown, diceResult;
int sum = 0;
for(diceThrown = 1; diceThrown <= i; diceThrown++){
scanf("%d", &diceResult); //limit this input to 2-12 only, how?
sum += diceResult;
}
if(sum >= 40){
sum = sum % 40;
if(sum == 12){
printf ("28\n");
} else if(sum == 35){
printf ("7\n");
} else{
printf ("%d\n", sum);
}
} else if(sum < 40){
if(sum == 12){
printf ("28\n");
} else if(sum == 35){
printf ("7\n");
} else{
printf ("%d\n", sum);
}
}
return 0;
}
Also just to clarify, that I'm still a beginner in programming (like only 2 months into C.SCi course), so if you could explain it to me like I'm not a expert that would be great.
scanf has no functionality to do what you want. You can just use an if to validate input.
if(scanf("%d", &diceResult) != 1 || diceResult < 2 || diceResult > 12) {
//handle invalid input here
}
If the input is invalid it is up to you what you want to do. You could ignore the input and ask the user to enter a valid number, you can quit the whole program or just ignore the error, or something else entirely.
You can also check the input repeatedly with an while:
while(scanf("%d", &diceResult) != 1 || diceResult < 2 || diceResult > 12) {
//prompt user to enter valid input here
}
As mentioned by chux, part of handling invalid input would be to cosume the invalid input and check for EOF.
The scanf("%d", &diceResult) != 1 will assure, that scanf actually read exactly one number and no parsing errors occurred.
Consider this:
#include <stdio.h>
int main(){
int x;
do
{
printf("give a number between [2-12]\n");
scanf ("%d",&x);
}
while(x<2 || x>12);
return 0;
}
You can use a do-while loop so that you only take the values that are between the 2-12 range. That way you can force the user to give an integer as an input that is in the range that you ask for, in that case from [2,12]. Otherwise the program will turn back and request a valid input again.
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;
}
My target output is after users entering a number >2 & <20 (result show) then program continue asking users enter another number. Or if users enters number <=2 or >=20, it will not show result but just re-asking users to enter number.
My Current Output: If I input number <=2 || >=20, it will re-ask. but if I enter number between 2 and 20. It will just stops which suppose to be keep asking for entering new numbers.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define MAX 20
int main(void)
{
unsigned int random_array[MAX][MAX];
unsigned int r, c, x, y;
do {
printf("Number Matrix in array ? ");
scanf("%d", &c);
system("cls");
r = c;
if (c>2 && c<20) {
r = c;
for (x = 0; x <= r - 1; ++x)
{
for (y = 0; y <= c - 1; ++y)
{
random_array[x][y] = -1;
}
}
for (x = 0; x <= r - 1; ++x)
{
for (y = 0; y <= c - 1; ++y)
{
if (x == y)
random_array[x][y] = 0;
else
if (x<y)
random_array[x][y] = 1;
printf("%4d", random_array[x][y]);
}
puts("");
}
system("pause");
}
} while (c<=2 || c >=20);
return 0;
}
Since you want to prompt the user for input regardless of what they last input, you probably need an infinite loop. For this, replace your line with the while condition to this:
} while (1);
This basically tells your program to loop infinitely.
Your codes
do
{
// show something
} while (c<=2 || c >=20);
means that it will stop after showing something if (c > 2 && c < 20), and that is exactly why your program quits after the condition is met.
To achieve your goal, consider using an infinite loop, and do different things using if-else inside the loop.
printf("Number Matrix in array ? ");
scanf("%d", &c);
system("cls");
if (c<=2 || c >=20)
{
continue;
}
else
{
// show something
}
The while condition should be while(c>2&c<20). But if you enter a number <=2 or >=20 the program will end and will not ask you for an input anymore. So the solution would be to use an infinite while loop and use break to end the loop when you want by using a condition.
A do-while loop will run the block of code once, then will repeat until the while conditional evaluates to false.
do{
//Stuff
}while (c > 20 || c < 2);
That would do the //Stuff part once, then it would do it again until c is either greater than 20 or less than 2.
What you want to do is surround the entire thing in an infinite loop, (either for(;;) or while(1)) so that it continues regardless.
But you also want to validate the input, so that's when you could use a do-while loop. When you're getting the scanf, you could do something like:
do{
printf("Enter c: ");
scanf("%d", &c);
}while (c > 20 or whatever);
Then you could make him keep putting in c until it's the desired input!
Hope this helps.
EDIT: Here's an example of putting the do-while inside the while:
while(1){
do{
printf("Enter a positive number: ");
scanf("%d", &aNum);
}while(aNum < 0);
printf("Your positive number is %d.\n", aNum);
}
That would ask a user for input, and if he puts in a negative number it would ask him again. If it's a positive number it would print, then go back to the start and ask him for an input again.
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;
}
I am doing a lab for an intro programming class
I have to make sure that an integer is entered. I thought this would do it but when I put in a letter it repeats in an endless loop.
I found this solution in another post
int num;
char term;
if (scanf("%d%c", &num, &term) != 2 || term != '\n')
printf("failure\n");
else
printf("valid integer followed by enter key\n");
But im not sure what I did wrong. Why is it not working in my code?
#include <stdio.h>
int main(void)
{
int oneVar;
char term;
double numOne;
double numTwo;
double sum;
double dif;
double quo;
double mult;
int checker = 1;
do
{
printf("Please choose one of the following:\n""1) Add\n""2) Subtract\n""3) Divide\n""4) Multiply\n""5) Quit\n");
if (scanf("%d%c" , &oneVar ,&term) != 2 || term != '\n')
{
printf ("This is not valid input\n\n");
checker = 1;
}
else if (oneVar == 5)
{
printf("Thank you. Goodbye.\n");
checker = 0;
}
else if (oneVar != 1 && oneVar !=2 && oneVar != 3 && oneVar != 4)
{
printf("This is not a valid input\n\n");
checker = 1;
}
else
{
printf("Please enter the first number:\n");
if (scanf("%lf%c" , &numOne ,&term) != 2 || term != '\n')
{
printf ("This is not valid input\n\n");
checker = 1;
}
printf("Please enter the second number:\n");
if (scanf("%lf%c" , &numTwo ,&term) != 2 || term != '\n')
{
printf ("This is not valid input\n\n");
checker = 1;
}
else if (oneVar == 1)
{
sum = numOne + numTwo;
printf("The sum is: %.2lf\n" ,sum);
checker = 0;
}
else if (oneVar == 2)
{
dif = numOne - numTwo;
printf("The difference is: %.2lf\n" ,dif);
checker = 0;
}
else if (oneVar == 3)
{
quo = numOne / numTwo;
printf("The quotient is: %.2lf\n" ,quo);
checker = 0;
}
else if (oneVar == 4)
{
mult = numOne * numTwo;
printf("The product is: %.2lf\n" ,mult);
checker = 0;
}
else if (oneVar == 5)
{
printf("Thank you. Goodbye.\n");
checker = 0;
}
}
} while (checker == 1);
return(0);
}
My prof posted this Im not sure how it helps but I thought it might help someone
To make sure that a user-input number is an integer you can use the notion of casting. Casting is a way to tell C to treat a variable as if it were a variable of a different type.
so, if I have something like this:
double myDouble;
myDouble = 5.43;
printf ("%d", (int) myDouble);
It will tell C to print myDouble, but to treat it like an integer. Only the 5 will be printed and you won't get any type mismatch errors. You can use casting to check to see if an input number is an integer by comparing the input to the (int) cast of the number. Something like this should work:
if(inputNum == (int) inputNum)
You'll still get 1.0 and 2.0 passing as valid numbers, but that is ok for now.
Why complicate things?
char x = 0;
scanf("%c", &x);
if (x >= 0x41 && x <= 0x7A)
printf("you entered a letter");
In ASCII table, letters have values between 0x41 ("A") and 0x7A ("z").
So, you just need to check the ASCII value of the input. :)
Using the %c to "consume" the end of line is not a good solution. If the user enters say:
123 abc<newline>
num will be 123, but term will be the space character. If you enter a letter rather than a number, the scan will stop without consuming any of the characters, the next input call will return due to the already buffered line, and may still consume nothing. Your program loops continuously because every input statement is failing to consume the newline and returns immediately. The standard input functions wait for a complete line before returning, if the line is not read completely, input functions do not need to wait.
There are a number of solutions, many of which such as the one you used are flawed, the method below, forces the input buffer to be flushed up to and including the newline.
int check = scanf( "%d", &num ) ;
while( getchar() != '\n' )
{
// do nothing
}
if( check != 2 )
printf("failure\n");
else
printf("valid integer followed by enter key\n");
If you use the %c format specifier at the end of the input, then a slightly different flush is necessary since the character input may be a newline:
int check = scanf( "%c", &ch ) ;
while( ch != '\n' && getchar() != '\n' )
{
// do nothing
}