#include <studio.h>
#include <string.h>

char *keypad[] = {
    "","",
    "ABC","DEF"
    "GHI","JKL"
    "MNO","PQRS"
    "TUV","WXYZ"
};
void generatecombination(char digits[],char output[],int index,int length){
    if(index == length) {
        output[index] = '\0';
        printf{"%s ",output);
        return;
    }
    int digit = digits[index] - '0';
    
    if (digit < 2 || digit > 9){
        printf("Invalid input\n");
        return;
    }
    char *letter = keypad[digit];
    for (int i = 0;letter[i]) != '\0';i++){
        output[index] = letter[i];
        generatecombinations
    }
    
}