Previous Topic
Course Outline
Next Topic
I considered loops as one of the things I find interesting during my first programming course. Haha. It’s really basic and uhmm...common. Together with if-else statements they can already build a powerful program.
So basically, loops are loops! It’s like looping over something (doing it over and over again) until a certain condition has been met (usually to reach the specified number of iterations).
There are three kinds of loops (not just in C but in most programming languages), the
for loop, the
while loop and
do-while loop.
For Loop
This I think is the most popular among the three.
A for loop statement consists of initialization, condition, something to do before the next iteration (oh my, what do they call this part? Haha) and of course, the body.
1
2
3
| for (int i = 0; i < 5; i++) {
printf("%d \n", grades[i]);
}
|
i is initialized to 0 before the first iteration. The condition is next check (the loop will iterate only if the condition is true). Is i < 5? Yes, so we iterate (i.e. execute the for loop body).
You’ve learned the printf() function before but let me explain what are new to you. When printing variables, placeholders are used by the printf() function. %d is the placeholder for integer values. Those placeholder are then replaced by the parameters provided (in order). So %d is to be replaced by the value of grades[i], which in the first iteration, is grades[0]. The \n will append a break (new) line after the array element.
Then, the something-to-do-before-the-next-iteration part is executed. Making i = 2. The initialization part is executed only once (before the first iteration). So now, the thing left before executing the body is to check if the condition still holds, i < 5 = 2 < 5 = true. It’s true so we proceed. And so on and so forth, until the condition fails which will happen in the sixth iteration where i = 5. This time, the condition no longer holds since i (which is now equal to 5) is no longer less than 5 and so we exit the for loop.
So yeah, basically the code above prints the values of our array grades.
While Loop
The for loop and the while loop are pretty similar. It’s just that the while loop is simpler when it comes to syntax.
while(<condition>) {
//some processing
}
So yeah, basically the while loop executes what's on its body provided that the condition holds true. Implementing the above for loop in a while loop, we have
1
2
3
4
5
| i = 0;
while(i < 5) {
printf("%d \n", grades[i]);
i++;
}
|
What you can do in a for loop, you can also do using a while loop and vice versa. I suggest to use for loop when you have to do some initialization (e.g.
i = 0) and post-iteration process–something that is not related to the loop body but is more on the iterator (e.g.
i++). Use while loop, on the other hand, when you don’t need these stuffs. Something like,
1
2
3
| while(!isGameOver()) {
// continue
}
|
Well you can also implement this in a for loop, like this
1
2
3
4
| // yeah, these can be blank
for (; !isGameOver(); ) {
//continue
}
|
But really, why? Haha.
Do-while Loop
Do-while is kind of different. As it name suggests, the body is executed (guaranteed, regardless of the condition) in the first iteration. The execution of the next iterations will then rely to the condition.
1
2
3
4
5
| i = 0;
do {
printf("%d \n", grades[i]);
i++;
} while (i < n);
|
Well, I can say it's bad example to appreciate a do-while statement. For loop is the most ideal for this kind of iteration.
Rule of thumb: Only use do-while when you want to execute the body once (in the first iteration) no matter what!
In my first programming course, I always use do-while loop in programs with user menu. When the program is launch, no matter what, the menu is displayed. The user can then choose whatever choice he/she wants. After executing the chosen case, the menu will be displayed again until the user choose to quit. Something like
1
2
3
4
5
6
7
8
9
10
11
| do {
system("cls"); // clear the screen at the start of every iteration
<some codes to print the menu>
switch(choice) {
case 1: <menu 1> break;
case 2: <menu 2> break;
case 3: break;
default: printf("\nThere's no such choice in the menu.\n\n"); break;
}
system("pause"); // explore to see what this line do
} while (choice!=3);
|
Previous Topic
Course Outline
Next Topic
