Question

In this programming assignment, you will write C code that performs recursion. For the purpose of this assignment, you will keep all functions in a single source file main.c. Your main job is to write a recursive function that generates and prints all possible password combinations using characters in an array.

• In your main() function you will first parse the command line arguments. You can assume that the arguments will always be provided in the correct format. Remember that the command line arguments are always strings. You will have to convert them to integers or individual characters for your use.
  • The program execution will be similar to ./a.out M c1 c2 c3 ... N
  • M represents the number of allowable characters in the password.
  • Based on the value for M, the next set of arguments will be the allowable characters. For example, if M = 3, then the next 3 arguments will be the characters allowed in the password. c1 = 'a', c2 = 'b', c3 = 'c'. The values of c1, c2, c3does not have to be in alphabetical order. It can be any of the 26 characters.
  • Another example, if M = 2, then there will only be 2 arguments: c1 = 'x', and c2 = 'y'.
  • N represents the maximum length of the password.
  • Using the value of M create a dynamic array of characters. Copy the next set of arguments c1, c2, ... into the array.
• Create a function called printPasswords().
  • This function will take in three parameters - N, M, and the array of allowable characters.
  • This function will not return anything.
  • This function will print all allowable passwords of length 1 <= length <= N, each on a separate line.
  • You can write as many helper functions as needed.

Following is an example output 1, when the program execution is ./a.out 3 a b c 2

a
b
c
aa
ab
ac
ba
bb
bc
ca
cb
cc

Following is an example output 2, when the program execution is ./a.out 2 a b 3

a
b
aa
ab
ba
bb
aaa
aab
aba
abb
baa
bab
bba
bbb

Answer 1

// C implementation

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

void convert_To_Len_th_base(int n,   int arr[],   int len,   int L)
{
   for (int i = 0; i < L; i++)
   {
       printf("%d",arr[n % len]);
       n /= len;
   }
   printf("\n");
}

// Print permuataions

void print(int arr[], int len, int L)
{
   // There are  (len)^l permutations
   for (int i = 0; i < (int)pow(len, L); i++) {
       // Convert i to len th base
       convert_To_Len_th_base(i, arr, len, L);
   }
}

// Driver code

int main(int argc,char *argv[])
{   
//argv[0] is file name
  
int len=atoi(argv[1]); //number of charcters
   int arr[len];
   for(int i=2;i<argc-1;i++)
   arr[i-2]=atoi(argv[i]);
   int L = atoi(argv[argc-1]); //length of permutation

   // function call
   for(int i=1;i<=L;i++)
   print(arr, len, i);

   return 0;
}