Question

I read in a char array with scanf and want to check if the length is bigger than 15.
It works only sometimes. (If not I get an error –> core dumped.)

My Code:

#include <stdio.h>

int checkArray(char string[], int length) {
    int i;
    for(i=0; string[i] != '\0'; i++);
    if(i > length) {
        return -1;
    }
    return 0;
}

int main ()
{
    const int length = 15;
    char x[15];
    scanf("%s", x);
    if(checkArray(x, length) == -1) {
        printf("max. 15 chars!");
        return 1;
    }
    return 0;
}

Answer 1

When scanf reads in a string longer than 14 characters (reserving one for the null terminator), it’s corrupting memory. Then, there are a couple problems with your checkArray() method:

int checkArray(char string[], int length) {
    int i;

    // This next line could as well be a call to `strlen`.
    // But you shouldn't let it access `string` when `i` is >= `length`. 
    for(i=0; string[i] != '\0'; i++);

    // This should be `>=`.  If `i` is 15, you accessed (in the loop above)
    // `string[15]`, which is past the end of the array.
    if(i > length) {
        return -1;
    }

    return 0;
}