For Loop: Getting to Know It and Some Gotchas

1. Introduction

Imagine you have a task: print "Hello!" to the screen ten times. Sure, you could write ten lines with Console.WriteLine("Hello!"); — but now you know about the while loop, so you can totally handle this.

But there's another loop — for, which repeats the needed action the exact number of times you want. And it can count by itself!

Here's a typical example:

for (int i = 0; i < 10; i++)
{
    Console.WriteLine("Hello!");
}

What does this code do? It prints "Hello!" to the screen exactly 10 times. No copy-paste, no wrist pain.

2. for Loop Syntax

The for loop has three main parts, written in parentheses after the for keyword:

for (initialization; condition; change)
{
    // Loop body
}

Let's break down each part in detail:

• Initialization — usually creating a counter variable to keep track of the repeats (int i = 0).
• Condition — checked before each iteration. If it's true, the loop body runs. If it's false, the loop ends. For example, i < 10.
• Change — this runs after each iteration. Usually increases or decreases the counter (i++).

You can draw a diagram:

3. Comparing for and while

Maybe it'll make more sense if I tell you that for is just another way to write a while loop.

We had a while loop:

int i = 0;					// Initialization of the loop variable
while(i < 10)				// Checking the loop continuation condition
{
    Console.WriteLine(i); 	// Useful action (loop body)
    i++					// Increasing the counter
}

We can write it as a for loop by just moving all the stuff that controls the loop logic:

for (int i = 0; i < 10; i++)  // Initialization; Condition check; Counter increase
{
    Console.WriteLine(i);		// Useful action (loop body)
}

Steps for both loops:

1. Initialization int i = 0; runs once before the loop.
2. Then the condition i <= 10 is checked
3. Then the loop's useful action Console.WriteLine(i);
4. Then the counter increases i++
5. Then it goes back to step 2.

4. for Loop Usage Examples

The simplest example

Let's print numbers from 1 to 5:

for (int i = 1; i <= 5; i++)
{
    Console.WriteLine(i);
}

Output:

1
2
3
4
5

Note: if you wrote i < 5, the last output would be 4.

Countdown

Want to feel like an astronaut? Let's do a countdown!

for (int i = 5; i > 0; i--)
{
    Console.WriteLine(i);
}
Console.WriteLine("Let's go!");

Output:

5
4
3
2
1
Let's go!

Loop step not equal to 1

You can change the counter by any number, not just 1:

for (int i = 0; i <= 10; i += 2)
{
    Console.WriteLine(i);
}
// Will print: 0 2 4 6 8 10

5. for Loop Variations

Multiple variables in the loop

Sometimes it's handy to track two variables at once. For example, let's print numbers from left to right and right to left:

for (int left = 1, right = 10; left <= 10; left++, right--)
{
    Console.WriteLine($"{left}  {right}");
}

Output:

1  10
2  9
3  8
...
10  1

Infinite for loop

If things get really wild (like your project is a perpetual motion machine in IT), you can make a "forever" for loop:

for (;;) // no initialization, no condition, no change
{
    Console.WriteLine("Work, work, and work some more!");
}

Warning: this loop will only end if there's a break, return, or throw inside. Don't use it without a good reason, or you might wake up an ancient demon — "Process not responding".

2

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Even Numbers from 2 to 20

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Countdown with a Message

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