Why null chars added in array?

I have an array which keeps chars of a string and want to find its suffixes. If i add 7 chars in the array the total number of chars should be 7*8/2 = 28. So the suffix_array limit should be 28. When i tried to create suffix array i noticed that array has null chars ass well. So my output is wrong. What is the reason of this?

#include <stdio.h>
#include <stdlib.h>

static char *suffix;

int main()
{
    char s[7] = {'c','o','n','n','e','c','t'};
    suffix = (char*) malloc(sizeof (char)*28);
    int j;
    static int k=0;
    j=k;
    for(int i=0; i<28; i++) {
        suffix[i] = s[j];
        printf("%c ", suffix[i]);
        if(j<7) {
            j++;
        }
        else {
            k++;
            j=k;
        }
            
    }
    
    return 0;
}

Output:

c o n n e c t  o n n e c t  n n e c t  n e c t  e c

>Solution :

You end up with j==7 (if (j<7) { j++; }), which is beyond the end of s.

Replace

if(j<7) {
    j++;
}
else {
    k++;
    j=k;
}

with

j++;
if(j==7) {
    k++;
    j=k;
}

Tips:

• It would be best to use strlen (once, up front) rather than hardcoding 7 and 28.

• You don’t really use suffix. But if you wanted to build a string in suffix, make sure to allocate one more char for the trailing NUL and to add the trailing NUL!

• const char *s = "connect"; would do fine.