Stopping an infinite while loop using scanf in c?

Question

I created a program that accepts 3 numbers separated by comments which I will use to do some calculations. It will accept user input for these numbers and I'm using scanf to accept that.

Here is what I have so far:

#include <stdio.h>
#include <math.h>
#include <ctype.h>
#include <stdbool.h>

int main(void)
{
    float a, b, c;

    bool continue_program = true;

    while (continue_program) {
        printf("Enter your coordinates: ");
        scanf("%f,%f,%f", &a,&b,&c);
        if(isdigit(a) && isdigit(b) && isdigit(c)){
            printf("Success!");
        } else {
            printf("Try again!");
        }
    }
}

Example Output:

Try again!Enter your coordinates: Try again!Enter your coordinates: Try again!Enter your coordinates: Try again!Enter your coordinates: Try again!Enter your coordinates: Try again!Enter your coordinates: Try again!Enter your coordinates: Try again!Enter your coordinates: Try again!Enter your coordinates: Try again!

I know that other people have also faced the same issue and went through the answer for those ones but couldn't get their implementations working for this code.

Iharob Al Asimi · Accepted Answer · 2015-01-16T16:25:16.447

2

You got it all wrong scanf() will return the number of arguments matched and you are not checking for that.

Also, the isdigit() function takes an integer, and returns non 0 if the ascii value of the passed argument corresponds to a digit.

To make your program stop when a condition is met, you should change the value of continue_program inside the loop, suppose you want to stop when scanf() didn't get 3 floating point numbers to read, it will return a value that is different from 3 so you can set that as the if condition

#include <stdio.h>
#include <math.h>
#include <ctype.h>
#include <stdbool.h>

int main(void)
{
    float a, b, c;

    bool continue_program = true;

    while (continue_program) {
        printf("Enter your coordinates: ");
        if (scanf("%f,%f,%f", &a, &b, &c) == 3){
            printf("Success!");
        } else {
            continue_program = false;
            printf("Try again!");
        }
    }
}

This solution is suggested following the comments by the OP

#include <stdio.h>
#include <math.h>
#include <ctype.h>
#include <stdbool.h>
#include <string.h>

int main(void)
{
    float a, b, c;
    char line[100];

    printf("Enter your coordinates: ");
    while (fgets(line, sizeof(line), stdin) != NULL) {
        size_t length;

        length = strlen(line);
        if (line[length - 1] == '\n')
            line[length - 1] = 0;
        if (strcmp(line, "0,0,0") == 0)
            break;
        if (sscanf(line, "%f,%f,%f", &a, &b, &c) == 3)
            printf("\tSuccess!\n");
        else
            printf("\tTry again!\n");
        printf("Enter your coordinates: ");
    }
}

edited Jan 16 '15 at 16:25

answered Jan 16 '15 at 15:55

Iharob Al Asimi

52,653
6
59
97

Okay knowing how it returns values helps a lot. How do I continue to keep asking them for coordinates? Setting the boolean to false will end the entire loop. – MathHopeful Jan 16 '15 at 16:10
It depends, when do you want to end the loop? – Iharob Al Asimi Jan 16 '15 at 16:13
@RandomMaker: Please explain when you want the program to stop. Is it after a "success" or after a "Failure"? – Support Ukraine Jan 16 '15 at 16:13
I don't understand all the down votes here... Anyway I'll do a +1 for this answer. – Support Ukraine Jan 16 '15 at 16:14
After a specific input is submitted. Specifically 0,0,0 – MathHopeful Jan 16 '15 at 16:16
I would suggest a different approach, because comparing `float`s with `0` is not as simple as you think. – Iharob Al Asimi Jan 16 '15 at 16:17
What approach would you suggest? – MathHopeful Jan 16 '15 at 16:21
@RandomMaker use `fgtets()` to read lines and then parse that with `sscanf()`. – Iharob Al Asimi Jan 16 '15 at 16:22
@RandomMaker: As iharob suggests floats are bad. Maybe you could use char instead. Then you could also use the isdigit() as in your first attempt. – Support Ukraine Jan 16 '15 at 16:22
1

@RandomMaker i will post a simple solution that I just wrote, check it out. – Iharob Al Asimi Jan 16 '15 at 16:24

score 1 · Answer 2 · answered Jul 02 '17 at 17:26

1

you are not updating the value of continue_program in your code. Hence its value remains true and hence the infinite loop.You have to update it to be false to stop it.

answered Jul 02 '17 at 17:26

bakarin

622
5
17

Stopping an infinite while loop using scanf in c?

2 Answers2