Question

I’m trying to append a char to string.

I tried

char *string = malloc(strlen(text) * sizeof (char));
for(i=0, i <n; i++)
{
    j = i;
    while (j <= strlen(text))
    {
        string[strlen(string)] = text[i];
        j = j + n;
    }
    string[strlen(string)] = '\0';
    printf("%s", string);
    string = "";
}

My goal is creating variations of text.I got segmentation fault with this code. What am i doing wrong?

EDIT: to be more clear what i want to do is:
lets say text = “asdfghjk”
And for n = 3 i want the following output:

afj
sgk
dh

Answer 1

This is what you want.

// Params
char *text = "asdfghjk";
int n = 3;
// Code
int i, j, k, len = strlen(text);
char *s = malloc((len + 1) * sizeof (char));
for (i = 0, i < n; i++) {
    for (j = i, k = 0; j < len; j += n) s[k++] = text[j];
    s[k] = 0;
}
printf("%s\n", s);

First of all, a string with terminating zero will take strlen()+1 bytes of space. Not just strlen().
Second, don’t ever use strlen() in a loop. Precalculate it in int and use it.
Third, you had an error: you had text[i], but meant text[j].
Fourth, as authors of previous answers mentioned, you can not calculate a length of a string if it does not have terminating zero yet.
Fifth, you don’t need to clear a string after each iteration since overwriting its characters and adding new terminating zero will make it completely new string.