Loops

Take a look at the following program :

// file : rect.C
// This program draws a rectangle of #'s and X's on the screen.
// Again, kinda lame, but who cares?
#include <iostream.h>
int main()
{
  cout << "X#X#X#X" << endl;
  cout << "#     #" << endl;
  cout << "X     X" << endl;
  cout << "#     #" << endl;
  cout << "X     X" << endl;
  cout << "#     #" << endl;
  cout << "X     X" << endl;
  cout << "#     #" << endl;
  cout << "X     X" << endl;
  cout << "#     #" << endl;
  cout << "X     X" << endl;
  cout << "#     #" << endl;
  cout << "X     X" << endl;
  cout << "#     #" << endl;
  cout << "X     X" << endl;
  cout << "X#X#X#X" << endl;

 return(0);
}

Take note of all the repeated lines of code. It is silly to reproduce so many lines of code. There is a better way of doing it. Look at this :

// file : rect_while.C
// This program draws a rectangle of #'s and X's on the screen.
// Again, kinda lame, but who cares?
#include <iostream.h>
int main()
{
  int i;

  cout << "X#X#X#X" << endl;
  i=0;
  while (i<7)
  {
    cout << "#     #" << endl;
    cout << "X     X" << endl;
    i = i + 1;
  }
  cout << "X#X#X#X" << endl;

  return(0);
}

So, what did I do? I replaced just about all of the repeated code with a while loop. There is another way to make a loop. Check this out :

// file : rect_do_while.C
// This program draws a rectangle of #'s and X's on the screen.
// Again, kinda lame, but who cares?
#include <iostream.h>
int main()
{
  int i;

  cout << "X#X#X#X" << endl;
  i=0;
  do
  {
    cout << "#     #" << endl;
    cout << "X     X" << endl;
    i = i + 1;
  }
  while (i<7);
  cout << "X#X#X#X" << endl;

  return(0);
}

And much to your surprise (or chagrin), here's a third way of doing it :

// file : rect_for.C
// This program draws a rectangle of #'s and X's on the screen.
// Again, kinda lame, but who cares?
#include <iostream.h>
int main()
{
  int i;

  cout << "X#X#X#X" << endl;
  for (i=0 ; i<7 ; i=i+1)
  {
    cout << "#     #" << endl;
    cout << "X     X" << endl;
  }
  cout << "X#X#X#X" << endl;

  return(0);
}

What is different between these three methods of doing loops?

See the WHILE specs.

See the FOR specs.