try this code to decript 6543 to 9876.
Code:
#include<iostream>
#include<conio.h>
using std::cout;
using std::cin;
using std::endl;
int main()
{
// declare variables
int num,digit1,digit2,digit3,digit4,dcript1,dcript2,dcript3,dcript4;
// initialize variables
dcript1=0,dcript2=0,dcript3=0,dcript4=0;
// read integer
cout<<"\nEnter the integer to be decripted:\t";
cin>>num;
// separate integers
digit1=num%10;
num/=10;
digit2=num%10;
num/=10;
digit3=num%10;
num/=10;
digit4=num%10;
num/=10;
// print decripted digit
if((digit1<7||digit2<7)||(digit3<7||digit4<7))
{
dcript1=(10+digit1)-7;
dcript2=(10+digit2)-7;
dcript3=(10+digit3)-7;
dcript4=(10+digit4)-7;
cout<<"\nDecripted 4-digit integer:\t\t";
cout<<dcript4<<dcript3<<dcript2<<dcript1;
}
else
dcript1=(digit1-7)%10;
dcript2=(digit2-7)%10;
dcript3=(digit3-7)%10;
dcript4=(digit4-7)%10;
getch();
}