The leap year thing is troubling, eg 29-02-2009 is not a leap year but it still displays a day which it should not.

#include<iostream>
#include<conio.h>
using namespace std;
int main ()
{
      int d=0,m=0,y=0,r1=0,r2=0,r3=0,r4=0,l=0;
      cout<<"Enter day : ";
      cin>>d;
      cout<<endl;
      cout<<"Enter Month : ";
      cin>>m;
      cout<<endl;
      cout<<"Enter Year : ";
      cin>>y;
      cout<<endl;
    
       
    {  
      if(m==10||m==1)
      m=0;
      else if(m==2||m==3||m==11)
      m=3;
      else if(m==4||m==7)
      m=6;
      else if(m==9||m==12)
      m=5;
      else if(m==5)
      m=1;
      else if(m==6)
      m=4;
      else if(m==8)
      m=2;
      }
      
      
      
      
      if  ( y % 4 == 0 || y % 400 == 0 )
     { 
     
     r1=y-2000;
      r2=r1/4;
      r3=r1+6+d+m+r2;
      r4=(r3%7)-1;
      
      }
           
       else 
      {
      r1=y-2000;
      r2=r1/4;
      r3=r1+6+d+m+r2;
      r4=(r3%7);
           }
      

      
          switch(r4)
      { 
        case 0:printf("SUNDAY");break;
        case 1:printf("MONDAY");break;
        case 2:printf("TUESDAY");break;
        case 3:printf("WEDNESDAY");break;
        case 4:printf("THURSDAY");break;
        case 5:printf("FRIDAY");break;
        case 6:printf("SATURDAY");break;
        default:printf("NOT VALID");break;
      }
      getche();
      }

delete lines 18 and 33 -- they serve no purpose.

For leap years, read this thread

Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.