Print all combination of a string using recursion in C

Question

I have an assignment to write code that printing all combinations of N char. For example, if the input is 3, the expected output must be "aaa aab aac aba ... ccc". But my code looping over and over again. Here's my code.

#include <stdio.h>

#ifndef MAX
#define MAX 5
#endif

void comb(char kar[], int size, int index) {
    // string = aaa
    // lim = 'd'
    char lim = 'a' + size;
    while (index != -1) {

        if (kar[size-1] != lim) { // != c
            for (int i = 0; i < size; i++) {
                printf("%s ", kar);
                kar[size-1]+=1;
            }
            return comb(kar, size, index);

        } else {

            while (kar[index-1] == lim && index != -1) {
                kar[index-1]='a';
                index--;
            }
            kar[index-1] += 1;

            return comb(kar, size, size);
        }
    }
}

int main(int argc, char const *argv[]) {
    int n;
    char kar[MAX];

    printf("Input N char : ");
    scanf(" %d", &n);

    for (int j = 0; j < n; j++) {
        kar[j] = 'a';
    }

    comb(kar, n, n);

    return 0;
}

I'm a little bit confused and I have no idea where is the mistake. Thank you.

OT: Hint: dont write 97 but 'a'. It's mor ereadable and clearly shows your intention. — Jabberwocky
– Jabberwocky, Commented Apr 21, 2020 at 11:51
Slightly OT: zero initialize the kar array like this: char kar[MAX] = { 0 };, otherwise you will most likely print garbage. — Jabberwocky
– Jabberwocky, Commented Apr 21, 2020 at 11:58
You only ever pass n, index, and size as the index argument, and you never assign to it within comb, so it's hard to see how index != -1 could ever become false. — 500 - Internal Server Error
– 500 - Internal Server Error, Commented Apr 21, 2020 at 12:34

Arief G · Accepted Answer · 2020-04-21 14:10:54Z

1

The problem has been solved. I changed some elements in the comb() and added the pow() function to define the recursion limit.

int comb(char kar[], int size, int index, int limit) {

    char lim = 97 + size;
    int limit_value = pow(size,size);
    if(limit == limit_value){
        return 1;

    } else {

        if (index < size-1) {
            printf("%s ", kar);
            kar[size-1]+=1;
            return comb(kar, size, index+1, limit+1);

        } else {
            int cek = index;
            printf("%s ", kar);
            while (kar[cek] == lim-1 ) {
                kar[cek]=97;
                cek-=1;
            }
            kar[cek] += 1;

            return comb(kar, size, 0, limit+1);
        }
    }
}

answered Apr 21, 2020 at 14:10

Arief G

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