Control Flow›Core· 30 min read

Repeating with for Loops

A for loop repeats code a set number of times — perfect for counting.

What you will learn

Write a for loop with start, condition and step
Use the loop counter inside the loop
Count up and count down

Why loops?

Imagine printing the numbers 1 to 5. You could write five println lines — but what about 1 to 1000? A loop repeats a block of code so you do not have to.

A for loop is ideal when you know how many times to repeat. It has three parts inside the brackets:

A for loop counting 1 to 5

for (int i = 1; i <= 5; i++) {
    System.out.println("Count: " + i);
}

Note: Output: Count: 1 Count: 2 Count: 3 Count: 4 Count: 5 The three parts are: start (int i = 1), keep going while (i <= 5), and step (i++ adds 1 each time). The loop stops when i becomes 6 because the condition is no longer true.

Reading the three parts

Part	Example	Meaning
Start	`int i = 1`	Runs once, before the loop begins
Condition	`i <= 5`	Checked before each round; loop runs while true
Step	`i++`	Runs after each round (here, add 1)

The i++ is shorthand for i = i + 1. The counter i is a normal variable you can use inside the loop — that is how we printed it.

Counting down

A countdown using i--

for (int i = 5; i >= 1; i--) {
    System.out.println(i);
}
System.out.println("Lift off!");

Note: Output: 5 4 3 2 1 Lift off! This time we start at 5, keep going while i >= 1, and i-- subtracts 1 each round. After the loop finishes, the last line runs once.

Watch out: Beware the infinite loop. If the step never makes the condition false (for example, counting up but using i--), the loop runs forever. Always check that the loop will eventually stop.

Tip: Programmers usually start counting from 0, not 1, because arrays (next-but-one lesson) are numbered from 0. So for (int i = 0; i < 5; i++) is extremely common.

Q. In for (int i = 1; i <= 3; i++), how many times does the loop body run?

Answer: It runs for i = 1, 2 and 3 — three times. When i becomes 4 the condition i <= 3 is false, so the loop stops.

✍️ Practice

Print the even numbers from 2 to 10 using a for loop (hint: step by 2 with i += 2).
Use a loop to add up 1 + 2 + ... + 10 and print the total.

🏠 Homework

Write a program that prints the times table of a number the user enters (for example, 7 x 1 up to 7 x 10).