Prmutations

I have the following algorithm for listing permutations but i cannot properly implement in C program:-

Code:

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Algorithm Perm(a,k,n)
{
    if (k = n) then write (a[1:n]); // output permutation
    else // a[k:n] has more than one permutation
            //  Generate these recursively
            for i := k to n do
            {
                    t := a[k]; a[k] := a[i]; a[i] := t;
                    Perm(a,k+1,n);
                    // All permutations of a[k+1:n]
                    t := a[k]; a[k] := a[i]; a[i] := t; 
              }
}

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I have coded the following but it does not work:-

Code:

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

void Perm(char[],unsigned,unsigned);

void Perm(char a[],unsigned k,unsigned n)
{
    if(k == n-1)
          printf("%s\n",a);
    else
    {
                for(unsigned i = k;i < n;i++)
          {
                  char t = a[k]; a[k] = a[i]; a[i] = t;
                  Perm(a,k+1,n-1);
                  t = a[k]; a[k] = a[i]; a[i] = t;
            }
    } 
}

int main(void)
{
        unsigned n;
        char *a;
       
        printf("Enter the size of the number : ");
        scanf("%u",&n);
       
        a = (char*)malloc(n*sizeof(char));
       
        printf("\nEnter the number : ");
        scanf("%s",a);
                   
        Perm(a,0,n-1);
       
        system("pause");
        return 0;
}

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Mostly, you have a problem with off by 1s.

Your biggest mistake is here

Code:

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Perm(a,k+1,n-1);

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In particular, you are decreasing n each recursive call, but n itself is supposed to be the length of a, but the length of a is unchanged. Otherwise, there are two more off by 1s, but you should be able to figure it out by just trying small example cases, like permuting the first 3 numbers.