Basics of Programming Part 4: Loops

the best use of a for loop. ever.

Part 1: Variables  | Part 2: Functions  |  Part 3: Operators

Loops. I like them. They make things much easier by allowing me to do less work. Loop work by doing an action multiple times without you having to write it again and again. The above cartoon from Bill Amend's FoxTrot does a great job of explaining how and why a FOR LOOP can be used. Here’s the code from the strip:

int main(void)

{

     int count;

     for(count = 1; count <= 500; count++)

           printf(“I will not throw paper airplanes in class.”);

     return 0;

}

You should be able to recognize the first line from our talk on functions. int means this will be what’s returned by the function, main is the name of the function, (void) is basically saying that main cannot have any parameters, which we might not have covered. I don’t remember.

The next line declares an integer variable of count, which will be used in the for loop.

The next line is the FOR LOOP and it might be a bit confusing. Let’s break it down into simpler thought first. Here’s the bits:

for() is the function name

count = 1 sets our variable to 1

count <= 500 check to make sure that count is less than or equal to 500

count++ is adding one (1) to our count variable

printf() is the action we preform after we do this count check

Make note that the prinf() is not enclosed in brackets. Even though functions have brackets, this is allowable because there is only one line of code inside that function. If we were to put anything else in there, say another printf() then we would have to use the brackets. I tend to use brackets regardless of the line count, simply because I never know when I’ll need to add more lines into a function. I believe general philosophy of programmers is to not do this as it makes the code pretty long and ugly, but they’re wrong. :P

Moving on. Let’s get into the nitty-gritty of what a for loop is really doing. We first set a variable count to 1. We then check to see if count is less than/equal to 500. If it is then we add 1 to count (++ means add one, -- means subtract one). Then we would print out “I will not throw paper airplanes in class.” Then the loop starts again. It will continue to print out this phrase until it has reached 500. On the 501^st loop it will stop printing and then move on to the next step in the function:

return 0 just returns a false value to our main function

And that’s a for loop. If you understood what I was explaining, then you’ll now understand the FoxTrot comic. Jason, the boy in the strip, was told to write “I will not throw paper airplanes in class.” 500 times. Instead of writing that line 500 times he automated it so the “computer” would simply print out the line 500 times. 

With just two lines of code you can save a whole bunch of copy/paste and more importantly your time so instead of this:

printf(“I will not throw paper airplanes in class.”);

printf(“I will not throw paper airplanes in class.”);

printf(“I will not throw paper airplanes in class.”);

printf(“I will not throw paper airplanes in class.”);

printf(“I will not throw paper airplanes in class.”);

printf(“I will not throw paper airplanes in class.”);

printf(“I will not throw paper airplanes in class.”);

printf(“I will not throw paper airplanes in class.”);

printf(“I will not throw paper airplanes in class.”);

printf(“I will not throw paper airplanes in class.”);

x 50

You simply write this:

for(count = 1; count <= 500; count++)

           printf(“I will not throw paper airplanes in class.”);

Hopefully you understand what a for loop is and what you can do with it. But before we go let’s take a look at a different type of loop, called the WHILE LOOP. Instead of using numbers like we did in the for loop this will check a condition. Here’s a small while loop:

while(!gamePaused)

{

hero.controls();

     hero.move();

     monster.move();

     game.controls();

}

haveParty();

Now this isn’t real code as we haven’t actually defined our functions but here’s the breakdown. The first line is looking to make sure that the game is not paused. If it is running then it will allow controller input for our hero, both the hero and monsters to move, as well as checking to see if the controller is being used for game systems, like pausing the game for instance. Then if the game is still not paused it will run through everything that’s in the while loop again. It will continue to do this until something changes the variable gamePaused from false to true. Then the function will be completed and the next line of code will run, meaning the computer will have a party! Yay!

This might not be as cut and dry as the for loop, but while loops pretty much run everything, whether it’s behind the code or a part of it. Games are built around constantly updating and a while loop does just that. So long as the condition is met, it will continue to run.

Well, that’s it for this one. I’m hoping to have something else to write about early next week, but I have to decide what else to cover in a basics course. Until next time, God bless and code everyday!

Part 1: Variables  | Part 2: Functions  |  Part 3: Operators