Question

I continue to learn programming in C, and today I met a problem.
In my program, a user must enter a value of time in minutes, and my program will calculate it seconds(very simple, actually). But I want to set a rule, that time cannot be negative. So I used this code:

    if(a<=0)
    {
        printf("Time cannot be equal to, or smaller than zero, so the program will now terminate\n");
        exit(EXIT_FAILURE);
    }

but now, I don`t want to terminate my program, I want it to return to the state when a user has to enter a value.

I had a problem with terminating my program, but some search helped me, however I did not get any result searching how to restart my program.

This is the text of my program(I am working on Linux):

#include<stdio.h>
#include<stdlib.h>
main()
{
    float a;
    printf("\E[36m");
    printf("This program will convert minutes to seconds");
    getchar();
    printf("Now enter your time in minutes(e.g. 5):");
    scanf("%f", &a);
    printf("As soon as you will press the Enter button you`ll get your time in seconds\n");
    getchar();
    getchar();


    if(a<=0)
    {
        printf("Time cannot be equal to, or smaller than zero, so the program will now terminate\n");
        printf("\E[0m");
        exit(EXIT_FAILURE);
    }
    else
    {
        float b;
        b=a*60;
        printf("\E[36m");
        printf("The result is %f seconds\n", b);
        printf("Press Enter to finish\n");
        getchar();
    }
    printf("\E[0m");
}

P.S. I don`t know how to correctly name this function, so I call it restart, maybe it has a different name?

Answer 1

Both the solutions that have been posted work, but I personally like this approach better:

// ...
printf("Now enter your time in minutes(e.g. 5):");
scanf("%f", &a);

while(a <= 0){
   printf("Time cannot be equal to, or smaller than zero, please enter again: ");
   scanf("%f", &a);
}

I think it is more clear, and it gives the opportunity to have an error message and a regular message independent of each other.