Lesson 3: Loops



This is the third installment of the Lessons in C programming tutorials created by me,

Alexander.  In this lesson I will cover loops.  Loops basically do what it sounds like,

loop.  If you have read lesson 2 you should understand some Boolean expressions.  If you do

not, you should read it again.  When working with loops it is important to understand truth

and false.  Maybe you should try doing some truth tables with problems.



There are basically 3 types of loops.  FOR, WHILE, DO WHILE  Each of them has their uses.

They are all outlined below.



FOR - FOR loops are the most useful type, I believe.  The layout is for(variable

initialization, conditional, incrementing variable)  It is very versatile, and the layout

can be changed somewhat.  Basically, the variable initialization allows you to either

declare a variable and give it a value, or give a value to another variable.  Second, the

conditional statement.  What it does is it says that while the conditional is true then it

would do what in is in the body.  Third, the incrementing variable section.  It does not

have to increment a variable.  It can decrement, which is subtracting one, or it can

perform various other manipulations on the variable.

		

	Ex. #include <iostream.h>  //We only need one header file

					

		void main()		//We always need this 

		{ 

		                             //The loop goes while x<100, and x has one 

		  for(int x=0;x<100;x++)/*THE LOOP*/ //added to it every time the loops 

		  {

		    cout<<x<<endl;           //Outputting x

	      }                       	

	    }



This program is a very simple example of a for loop.  x is set to zero, while x is less

than 100 do cout<<x<<endl; add 1 to x until the loop ends.  Pretty simple to understand,

but it is a very powerful loop, and much better than WHILE and DO WHILE loops.



WHILE - WHILE loops are very simple, but not as useful as FOR loops.  The basic structure

is...WHILE(true) then do whatever is in the body.  The truth could be x==1 or while(x!=7)

(x does not equal 7)



	Ex. #include <iostream.h> //We only need this header file



		void main()		//Of course... 

		{ int x=0;  		//Don't forget to declare variables

		  while(x<100)		//While x is less than 100 do 

		  { 

		  cout<<x<<endl;	//Same output as the above loop 

		  x++;		//Adds 1 to x every time it repeats 

		  } 

		}



This was another pretty simple example, but it is longer than the above FOR loop, showing

why I like for better than while, though while is a very easy loop to use, so if you are

having trouble then you can use it, but try to use for.



DO WHILE - DO WHILE loops are useful for only things that want to loop at least once.

          basically it goes DO { THIS } WHILE(TRUE)



Now, it is your turn to try and do a loop!  make a DO WHILE loop that does what the above

programs do...output 0 to 99!  It is not hard, if you have trouble email me at

lallain@concentric.net and I will give you some help... Best of luck :)  Check back again for

more programming in C!



Note: My homepage is http://www.cprogramming.com.  My email is lallain@concentric.net.  Please

email me with comments and or suggestions.  If you want to use this on your own site please

email me and add a link to http://www.cprogramming.com.  Thanks :)