C - Segmentation Fault

Question

I keep getting a Segmentation Fault error when I run the program with a txt files with 5 numbers. First number is 5 (size of array) and then 0 1 2 3 4 It compiles just fine when I gcc -c *.c.

Main file

#include <stdio.h>
#include <stdlib.h>
#include "my.h"
int main(int argc, char *argv[])
{
 char* file = argv[1];
 int n;
 int* a;
 int i,j;

FILE *fp;
fp = fopen(file, "r"); // open file

    fscanf(fp, "%d", &n); //scans for the first value for n 

    a = calloc(n, sizeof (int));
    int num;

    for (i =0; i<n - 1; i++) //stores and reads value 
    {
        fscanf(fp, "%d", &num);
        a[i] = num;
    }
    fclose(fp);
    int* b;
    b = f(a, n);
    displayValue(b);

 return 0;
}

Functions

#include <stdio.h>
#include <stdlib.h>
#include "my.h"
int* f(int* a, int n)
{

    //odd-even sort
    int h,j, c;
    for ( h = 0; h < n - 1; h++)
    {
        if(a[h]%2==0)
        {
        if (a[h] > a[h + 1])
            {
                int temp = a[h];
                a[h] = a[h +1];
                a[h + 1] = temp;
            }
        }
    }

    for (j = 0; j < n - 1; j++)
        {
            if(a[j]%2!=0)
            if (a[j] > a[j + 1])
            {
                int temp = a[j];
                a[j] = a[j +1];
                a[j + 1] = temp;
            }
        }
return a;
}

void displayValue(int* b)
    {
    int index = 0;
        while (0 == 0)
        {
            printf("Enter the index: ");
            scanf("%d", &index);
            if (index == -1)
                exit(0);
            else
                printf("%s", &b[index]);
        }
    }

Header

int main(int argc, char *argv[]);
int* my(int* a, int n);
void displayValue(int* b);

Answer 1

C is dangerous. Anything that can go wrong will go wrong.

Always check the return values of function calls, and handle possible failures.

Each of the standard library function calls has a man page (if you have trouble finding it, use man -a <function>). The man pages document the possible return values and their meanings. man is your fried, get used to studying it; it is a valuable resource.

Beware of conditions that result in "undefined behavior".