explaination of a code.

[slychronic]

hie guys have a textbook that am reading there is a code that i need some help understanding better....can anyone explain to me line by line whats really going on....

No need to explain the main function though.......its a program that calculates permutation of whole numbers...Cheers!

#include<iostream>
#include<conio.h>
#include<string.h>
using namespace std;

int count=0;


void dis(char a[],int n)
{
   for(int jk=n-1;jk>=0;jk--)
     {
                 cout<<a[jk];
    }
cout<<" ";
}



void shift(char a[],int n)
{
 char s;
 s=a[n-1];
 for(int i=n-1;i>0;i--)
   a[i]=a[i-1];
 a[0]=s;
}


void per(char a[],int m,int n)
{
for(int i=0;i<m;i++)
  {
   if(m>1)
   {
    shift(a,m);
    per(a,m-1,n);    
   }
   else
    {
    dis(a,n);       
    count++;
    }
   }
}


void main()
{
  int n;
 

  cout<<"Enter a whole number : ";
  cin>>n;

  char *a = new (char[n]);

  for(int i=0;i<n;i++)
     a[i] = n-i+48;



  cout<<"Possible permutations are :  ";
  per(a,n,n);
  cout<<"Total No Of Permutations Is "<<count;
  _getch();
}

[jonsca]

Use of the "dis" function (or a series of cout statements) at strategic points in your program will let you trace it through step by step (or step through it using a debugger if you have one). If you then write a couple of sentences, someone can look at it for you and tell you if you are correct.

I know it's not the answer you wanted, but you'll learn a lot more doing it that way.

Also, main() always returns an int, according to the standard.

[slychronic]

ok i did what you said i should do and i managed to make out these comments ..could you help me add flesh to them and probably make more??

//header files
#include<iostream>
#include<conio.h>
#include<string.h>
using namespace std;

int count=0;

//func to display the sequence
void dis(char a[],int n)
{
   for(int jk=n-1;jk>=0;jk--)
     {
                 cout<<a[jk];
    }
cout<<" ";
}

//function to left shift last n elements
//of the array by one position
void shift(char a[],int n)
{
 char s;
 s=a[n-1];
 for(int i=n-1;i>0;i--)
   a[i]=a[i-1];
 a[0]=s;
}

//func to find all possible arrangements
void per(char a[],int m,int n)
{
for(int i=0;i<m;i++)
  {
   if(m>1)
   {
    shift(a,m);
    per(a,m-1,n);    //genetrating the tree
   }
   else
    {
    dis(a,n);       //displaying the leaf nodes of the tree
    count++;
    }
   }
}

[jonsca]

Looks pretty good so far.

1)Which way does "dis" display the elements?

2)Denote the type of function "per" (hint, line 38)