So, I have a Program which checks if a Triangle is valid, here is the code.
#include <stdio.h>
int main()
{
int side1, side2, side3;
/* Initially assume that the triangle is not valid */
int valid = 0;
/* Input all three sides of a triangle */
printf("Enter three sides of triangle: \n");
scanf("%d%d%d", &side1, &side2, &side3);
if((side1 + side2) > side3)
{
if((side2 + side3) > side1)
{
if((side1 + side3) > side2)
{
/*
* If side1 + side2 > side3 and
* side2 + side3 > side1 and
* side1 + side3 > side2 then
* the triangle is valid. Hence set
* valid variable to 1.
*/
valid = 1;
}
}
}
/* Check valid flag variable */
if(valid == 1)
{
printf("Triangle is valid.");
}
else
{
printf("Triangle is not valid.");
}
return 0;
}
But what I want to do is add a Prompt to ask how many triangles to check, so I would add something like this
#include <stdio.h>
int main()
{
int repeats;
/* Input the amount of repeats */
printf(" the amount of repeats: \n");
scanf("%", &repeats);
...
The amount of entered should be the amount of triangles the user wants to check.
Bonus Question: How to check that the user entered only a number and no letter.
Thanks in advance.
The
scanf("%", &repeats);
must've been
scanf("%d", &repeats);
as repeats is an int.
You could just place the block of code that you want to execute repeatedly in a loop like
for(i=0; i<repeats; ++i)
{
//your code
}
To check whether the user entered a number and not a character check the return value of scanf(). It returns the number of successful assignments it did.
Since the format specifier is %d in
scanf("%d", &repeats);
scanf() expects an integer. But if a character was given out instead, it won't assign (and would return 0 in this case) and the input (which is not a number) will remain unconsumed in the input buffer.
if( scanf("%d", &repeats)!=1 )
{
//value was not read into 'repeats'
}
This might be of interest to you.
Now if the invalid input remains in the input buffer, it can cause problems with the next scanf(). So it must somehow be consumed.
You could do something like
int ch;
while( (ch=getchar())!='\n' && ch!=EOF );
This would consume from the input buffer till the next new line (\n).
Have a look here.
And your
if((side1 + side2) > side3)
{
if((side2 + side3) > side1)
{
if((side1 + side3) > side2)
{
valid = 1;
}
}
}
could be made
if( (side1 + side2)>side3 && (side2 + side3)>side1 && (side1+side3)>side2 )
{
valid = 1;
}
and you don't really need the extra parenthesis because arithmetic operators have greater precedence than relational operators which in turn have greater precedence than logical operators.
Look here.
you could achieve that simply by wrapping a do while around your code so that it looks something like that
#include <stdio.h>
int main()
{
int repeats = 0, counter = 0;
/* Input the amount of repeats */
printf(" the amount of repeats: \n");
scanf("%d", &repeats);
do {
...
check here if its a triangle
...
counter++;
} while(counter < repeats);
Related
I have a weird issue. I ask a user to enter a number between 1 and 15. Then I would ask the user would the like to get the factorial value of the number using either recursive or a for loop.
When they answer that question the inputted value goes to 0. If I remove the question for testing purpose the value stays the value the user inputted.
#include <stdio.h>
int recursive(int);
int nonRecursive(int);
int main()
{
/* Variables */
int numberSelected, returnedValue;
char answer;
do
{
/* Request a number between 1 and 15 */
printf("Please enter a number between 1 and 15: ");
scanf("%d", &numberSelected);
printf("%d\n", numberSelected); /* This prints out the user's number */
}while(numberSelected < 1 || numberSelected > 15); /* Loops if the value is not between 1 and 15 */
/* Ask user if they want to return a recursive value or a value calculated manually */
printf("Would you like a recusive value of the number you entered? Y or N: ");
scanf("%s", &answer);
if(answer == 'y' || answer == 'Y')
{
printf("%d\n", numberSelected); /* Here it resets to 0 */
returnedValue = recursive(numberSelected); /* Returns the recursive value */
printf("The recursive value of %d is %d\n", numberSelected, returnedValue);
}
else
{
printf("%d\n", numberSelected); /* Here it resets to 0 also*/
returnedValue = nonRecursive(numberSelected); /* Returns the value from for loop */
printf("The non recursive value of %d is %d\n", numberSelected, returnedValue);
}
return 0;
}
/* Get value using recursive */
int recursive(int n)
{
if (n == 0)
return 1; // Base case
else
return n * recursive(n - 1);
}
/* Get value using for loop */
int nonRecursive(int n)
{
int i;
int fact = 1;
for(i = 1; i <= n; i++)
{
fact *= i;
}
return fact;
}
Thank you for the help
scanf("%s", &answer);
is wrong. %s is for reading strings (null-terminated sequence of characters), but answer has only room for 1 character, so out-of-bound write will occur when strings with one or more characters is read. It may break data around that.
The line should be
scanf(" %c", &answer);
Use %c, which reads single character.
Add a space before %c to have scanf() ignore whitespace characters.
writing a program that will be finding min, max, avg of values entered by user. Having trouble writing something that will check to make sure there are only postive integers entered and produce an error message. heres my for statement that is reading the input so far:
for (int value = 0; value <= numofvals; ++value) {
printf("Value %d: %f\n", value, val_input);
scanf("%f", &val_input);
}
mind you I've been learning code for about 3 weeks and was just introduced to loops this week so my understanding is rudimentary at best!
First, don't use scanf. If stdin doesn't match what it expects it will leave it in the buffer and just keep rereading the same wrong input. It's very frustrating to debug.
const int max_values = 10;
for (int i = 0; i <= max_values; i++) {
int value;
if( scanf("%d", &value) == 1 ) {
printf("Got %d\n", value);
}
else {
fprintf(stderr, "I don't recognize that as a number.\n");
}
}
Watch what happens when you feed it something that isn't a number. It just keeps trying to read the bad line over and over again.
$ ./test
1
Got 1
2
Got 2
3
Got 3
foo
I don't recognize that as a number.
I don't recognize that as a number.
I don't recognize that as a number.
I don't recognize that as a number.
I don't recognize that as a number.
I don't recognize that as a number.
I don't recognize that as a number.
I don't recognize that as a number.
Instead, use fgets to reliably read the whole line and sscanf to parse it. %f is for floats, decimal numbers. Use %d to recognize only integers. Then check if it's positive.
#include <stdio.h>
int main() {
const size_t max_values = 10;
int values[max_values];
char buf[1024];
size_t i = 0;
while(
// Keep reading until we have enough values.
(i < max_values) &&
// Read the line, but stop if there's no more input.
(fgets(buf, sizeof(buf), stdin) != NULL)
) {
int value;
// Parse the line as an integer.
// If it doesn't parse, tell the user and skip to the next line.
if( sscanf(buf, "%d", &value) != 1 ) {
fprintf(stderr, "I don't recognize that as a number.\n");
continue;
}
// Check if it's a positive integer.
// If it isn't, tell the user and skip to the next line.
if( value < 0 ) {
fprintf(stderr, "Only positive integers, please.\n");
continue;
}
// We got this far, it must be a positive integer!
// Assign it and increment our position in the array.
values[i] = value;
i++;
}
// Print the array.
for( i = 0; i < max_values; i++ ) {
printf("%d\n", values[i]);
}
}
Note that because the user might input bad values we can't use a simple for loop. Instead we loop until either we've read enough valid values, or there's no more input.
Something easy like this may work for you:
int n;
int ret;
for (;;) {
ret = scanf("%d", &n);
if (ret == EOF)
break;
if (ret != 1) {
puts("Not an integer");
for (;;)
if (getchar() == '\n')
break;
continue;
}
if (n < 0) {
puts("Not a positive integer");
continue;
}
printf("Correct value %d\n", n);
/* Do your min/max/avg calculation */
}
/* Print your results here */
This is just an example and assumes you do not need to read floating point numbers and then check if they are integers, as well as a few other things. But for starters, it is simple and you can work on top of it.
To break out of the loop, you need to pass EOF (typically Ctrl+D in Linux/macOS terminals, Ctrl+Z in Windows ones).
An easy and portable solution
#include <limits.h>
#include <stdio.h>
int get_positive_number() {
char buff[1024];
int value, ch;
while (1) {
printf("Enter positive number: ");
if (fgets(buff, 1023, stdin) == NULL) {
printf("Incorrect Input\n");
// Portable way to empty input buffer
while ((ch = getchar()) != '\n' && ch != EOF)
;
continue;
}
if (sscanf(buff, "%d", &value) != 1 || value < 0) {
printf("Please enter a valid input\n");
} else {
break;
}
}
return value;
}
void solution() {
// Handling malformed input
// Memory Efficient (without using array to store values)
int n;
int min = INT_MAX;
int max = INT_MIN;
double avg = 0;
printf("Enter number of elements: ");
scanf("%d", &n);
getc(stdin);
int value;
for (int i = 0; i < n; i++) {
value = get_positive_number();
if (value > 0) {
if (min > value) {
min = value;
}
if (max < value) {
max = value;
}
avg += value;
}
}
avg = avg / n;
printf("Min = %d\nMax = %d\nAverage = %lf\n", min, max, avg);
}
int main() {
solution();
return 0;
}
Output:
Enter number of elements: 3
Enter positive number: 1
Enter positive number: 2
Enter positive number: a
Please enter a valid input
Enter positive number: -1
Please enter a valid input
Enter positive number: 1
Min = 1
Max = 2
Average = 1.333333
I am trying to design a program that calculates the average of any desired number of floats, until EOF. The program should also check if the input was correct and return "Wrong Input" when e.g. entering a string. The code I wrote works, but it gives wrong ouputs for the average. Can anyone tell me why?
#include <stdio.h>
int main(void) {
int times = 0;
float sum = 0;
float scan;
float avrg;
int scanvalue = 1;
while (scanvalue == 1) {
scanvalue = scanf("%f", &scan);
sum = sum + scan;
times++;
}
if (scanvalue == EOF) {
avrg = sum / times;
printf("The average is %f\n", avrg);
} else {
printf("Wrong input");
}
return 0;
}
Best regards.
You don't check scanvalue after scanf() and still use the value at scan which is messing up the average. Note that when scanf() returns EOF it will not modify scan, and thus it will still have its last value so you are adding the last value twice.
But if you enter invalid input at the beginning then the behavior is undefined, change it to
while ((result = scanf("%f", &value)) == 1) {
}
Also, I deliberately changed the names of your variables to illustrate a better way of naming them.
You need to check scanvalue after the scanf, otherwise times will be incremented even if you enter EOF and sum will get a wrong input, thus resulting the average being wrong/messed.
So you should change
while (scanvalue == 1) {
scanvalue = scanf("%f", &scan);
sum = sum + scan;
times++;
}
To
while (scanvalue == 1) {
scanvalue = scanf("%f", &scan);
if (scanvalue != 1)
break;
sum = sum + scan;
times++;
}
I'm trying to create a program where the program guesses what kind of number the user has in mind. First it will ask the user for a minimum and maximum number, for example 1 and 10(the number I have in mind should be between 1 and 10 then).
Lets say I have the number 4 in mind and the program will output a number. I can type in L for low, H for high or G for good.
If I type in L, the program should generate a number lower than the guessed number, for H it should guess an higher number. If I input G, the program should stop and print out how many times it guessed.
I have added my code below, what am I missing?
#include <stdio.h>
#include <stdlib.h>
int main() {
int minNumber;
int maxNumber;
int counter;
printf("Give min and max: ");
scanf("%d %d", &minNumber, &maxNumber);
//printf("%d %d", minNumber, maxNumber);
int num_between_x_and_y = (rand() % (maxNumber - minNumber)) + minNumber;
char input[100];
do {
printf("is it %d? ", num_between_x_and_y);
scanf("%s", input);
if (input == 'L') {
counter++;
}
if (input == 'H') {
counter++;
}
} while (input != 'G');
printf("I guessed it in %d times!", counter);
return 0;
}
I do not see any "counter" variable initialization
int counter = 1;
I do not see the new random number regeneration in the cycle, it should be something like:
do {
printf("is it %d? ", num_between_x_and_y);
scanf("%s", input);
if (input[0] == 'L') {
counter++;
maxNumber = num_between_x_and_y;
}
if (input[0] == 'H') {
counter++;
minNumber = num_between_x_and_y;
}
num_between_x_and_y = (rand() % (maxNumber - minNumber)) + minNumber;
} while (input[0] != 'G');
You can't use == to compare strings (which are multiple bytes).
Either do if (input[0] == 'L') to just compare the first letter the user entered to a literal value, or if (strcmp(input,"L") == 0) to compare everything the user entered to the 1 character string literal (to use strcmp you will need to add #include <string.h>
Also your code is missing other things, like counter should be set to presumably set to zero before you use it. I assume you haven't finished your code yet because you can't get the user input part to work.
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;
}