For a program that takes a single number from a user, how can you test several values at once and then output them to a text file?

Question

I have written a fairly simple program in C that takes an input n and computes the n'th number in the fibonacci sequence. When this program runs, you enter a number on your keyboard, and it prints out the result. My question is, I can only manually test one input at a time, to check for bugs. How can I write a program to test several inputs at the same time, and output this to a readable text file?

I have tried writing a program to run these tests, but I don't know how to make the program use my function which is written in a separate file. I appear to be able to only test one at a time, and When I output the result to a text file, I cannot read the text file either, it is empty.

Answer 1

The easiest solution would be to migrate your code to a function then call it in a loop:

#include <stdio.h>

long fib(long n) {
   // ...
}

int main() {
    long n = 2;
    for(long i = 0; i < n; i++)
        printf("%ld %ld\n", i, fib(i));
}

In order to so you will have to separate i/o (prompting user for input) from the function that implements the Fibonacci algorithm. This is a good design practice in general. You can build two programs (one interactive and one not), or a single program and for instance drive that with a command line argument:

int main(int argv, char argv[]) {
    if(argc == 2) {
        long n = atol(argv[1]);
        for(long i = 0; i < n; i++)
            printf("%ld %ld\n", i, fib(i));
        return 0;
    }
    printf("n? ");
    long n;
    if(scanf("%ld", &n) != 1) return 1;
    printf("%ld %ld\n", n, fib(n));
}

I suggest you print the data then redirect the stdout to a file. You will have to show us some code to figure out why your text output file feature is not working.