Mysterious Crash

[psukphranee]

So I am doing a problem from C How To Program 7th Edition by Deitel. The problem is 8.10 for those who might have access to the book.

In a nutshell, I am comparing strings up to n characters. The program funs fine however at the end it crashes. I cannot figure out why

#include <string.h>
#include <stdio.h>

int main(void){

    char *string1, *string2;

    int n, compare;

    puts("Enter a string");
    fgets(string1,20, stdin);

    puts("Enter a string");
    fgets(string2,20, stdin);

    puts("Enter the amount of characters to compare");
    scanf("%d",&n);

    compare = strncmp(string1, string2, n);

    if(compare == 0)
        printf("Strings compares are equal\n");
    else
        printf("string 1 is %s String 2\n", (compare > 0) ? "greater than" : "less than");

    printf("Ending ....\n");

    return 0;
}

[stahta01]

You NEED to allocate space for the C-string!!
Your pointers are pointer to random locations; of course it crashes sometimes.

This code creates to pointers that point to a random location; likely to a location that you do not own or a location you do own that gets over written.

char *string1, *string2;

Simple fix is this line instead

char string1[20+1], string2[20+1];

Tim S.

[psukphranee]

Thank You. You are right, it does crash SOMETIMES.