C :

#include<stdio.h>
int main()
{
 printf("Hello World! I'm a C++ program.\n");
 } 

C++ :

#include <iostream>
using namespace std;
int main ()
{
  cout << "Hello World!";
  cout << " I'm a C++ program.";
  return 0;
} 

Pascal :

begin
writeln('Hello World! I''m a C++ program.');
end.