Question

Can someone help me get a C algorithm to generate all letter combinations of length n?

I need the output to be like:

aaaaaaa
aaaaaab
aaaaaac
.
.
.
zzzzzzx
zzzzzzy
zzzzzzz



for(i = 0; i<length; i++){
    pass[i] = 'a';
}

while(1){
    for(j=0;j<26;j++){
        printf("%s\n",pass);
        pass[i] = (char)(pass[i]+1);
    }
    if(pass[i-1]==z)...
}
return 0;

Answer 1

Here’s a version using recursion:

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

void iterate(char *str, int idx, int len) {
    char c;

    if (idx < (len - 1)) {
        for (c = 'a'; c <= 'z'; ++c) {
            str[idx] = c;

            iterate(str, idx + 1, len);
        }
    } else {
        for (c = 'a'; c <= 'z'; ++c) {
            str[idx] = c;

            printf("%s\n", str);
        }
    }
}

#define LEN 3

int main(int argc, char **argv) {
    char str[LEN + 1];

    memset(str, 0, LEN + 1);

    iterate(str, 0, LEN);
}