For loop syntax in Java

Introduction

A for loop helps you repeat a set of actions many times without writing the same code again and again.

When you want to count from 1 to 10 and do something each time.

When you need to go through all items in a list or array one by one.

When you want to repeat a task a fixed number of times, like printing a message 5 times.

When you want to process each character in a word or sentence.

When you want to sum numbers from 1 to 100 automatically.

Syntax

Java

for (initialization; condition; update) {
    // code to repeat
}

initialization sets a starting point, like int i = 0;.

condition is checked before each loop; if true, the loop runs.

update changes the loop variable, usually increasing or decreasing it.

Examples

This prints numbers 0 to 4, counting up by 1 each time.

Java

for (int i = 0; i < 5; i++) {
    System.out.println(i);
}

This counts down from 10 to 1, printing each number.

Java

for (int i = 10; i > 0; i--) {
    System.out.println(i);
}

This prints even numbers from 0 to 8 by adding 2 each time.

Java

for (int i = 0; i < 10; i += 2) {
    System.out.println(i);
}

Sample Program

This program counts from 1 to 5 and prints each number with the word "Count:" before it.

Java

public class ForLoopExample {
    public static void main(String[] args) {
        for (int i = 1; i <= 5; i++) {
            System.out.println("Count: " + i);
        }
    }
}

Important Notes

The loop variable (like i) is usually declared inside the for loop.

If the condition is false at the start, the loop code will not run at all.

You can use any variable name, but i, j, and k are common for loops.

Summary

A for loop repeats code a set number of times.

It has three parts: start, condition to keep going, and how to change the counter.

Use it when you know how many times you want to repeat something.

Practice

1.

What is the main purpose of a for loop in Java?

easy

A. To define a new class

B. To make decisions based on conditions

C. To repeat a block of code a specific number of times

D. To store multiple values in a list

Solution

1. Step 1: Understand the role of a for loop

   A for loop is used to repeat code multiple times when the number of repetitions is known.

2. Step 2: Compare with other options

   Options A, B, and C describe other programming concepts, not loops.

3. Final Answer:

   To repeat a block of code a specific number of times -> Option C

4. Quick Check:

   For loop = repeat code fixed times [OK]

Hint: For loops repeat code a set number of times [OK]

Common Mistakes:

• Confusing for loop with if statement
• Thinking for loop stores data
• Mixing for loop with class definition

2.

Which of the following is the correct syntax for a basic for loop in Java?

for (int i = 0; i < 5; i++) {
    System.out.println(i);
}

easy

A. for (int i = 0; i < 5; i++) { System.out.println(i); }

B. for int i = 0; i < 5; i++ { System.out.println(i); }

C. for (int i = 0; i < 5; i++) System.out.println(i)

D. for (int i = 0; i < 5; i++) System.out.println(i); }

Solution

1. Step 1: Check the for loop syntax structure

   The correct syntax requires parentheses around initialization, condition, and increment, and braces to enclose the loop body.

2. Step 2: Validate each option

   for (int i = 0; i < 5; i++) { System.out.println(i); } has correct syntax with parentheses and braces. for int i = 0; i < 5; i++ { System.out.println(i); } misses parentheses. for (int i = 0; i < 5; i++) System.out.println(i) misses semicolon after println(i). for (int i = 0; i < 5; i++) System.out.println(i); } has an extra closing brace.

3. Final Answer:

   for (int i = 0; i < 5; i++) { System.out.println(i); } -> Option A

4. Quick Check:

   Correct for loop syntax = for (int i = 0; i < 5; i++) { System.out.println(i); } [OK]

Hint: For loop needs parentheses and braces for multiple statements [OK]

Common Mistakes:

• Omitting parentheses around loop control
• Missing braces for multiple statements
• Extra or missing braces

3.

What will be the output of the following Java code?

for (int i = 1; i <= 3; i++) {
    System.out.print(i + " ");
}

medium

A. 0 1 2

B. 1 2 3

C. 1 2 3 4

D. 3 2 1

Solution

1. Step 1: Analyze the loop range

   The loop starts at i=1 and runs while i is less than or equal to 3, so i takes values 1, 2, and 3.

2. Step 2: Determine the output

   Each iteration prints the current i followed by a space, so output is "1 2 3 "

3. Final Answer:

   1 2 3 -> Option B

4. Quick Check:

   Prints 1 to 3 with spaces = 1 2 3 [OK]

Hint: Check loop start, end, and print inside loop [OK]

Common Mistakes:

• Starting loop at 0 instead of 1
• Including extra number beyond 3
• Printing in reverse order

4.

Identify the error in the following for loop code snippet:

for (int i = 0; i < 5; i++)
    System.out.println(i);
}

medium

A. Extra closing brace } without matching opening brace

B. Incorrect loop condition syntax

C. Missing semicolon after i++

D. Variable i not declared

Solution

1. Step 1: Check loop syntax and braces

   The for loop has no opening brace but has a closing brace, which is unmatched and causes a syntax error.

2. Step 2: Verify other parts

   Semicolons and variable declaration are correct, and the loop condition syntax is valid.

3. Final Answer:

   Extra closing brace } -> Option A

4. Quick Check:

   Unmatched brace causes syntax error = Extra closing brace } without matching opening brace [OK]

Hint: Match every opening brace with a closing brace [OK]

Common Mistakes:

• Leaving unmatched braces
• Forgetting semicolons in loop header
• Not declaring loop variable

5.

How can you write a for loop in Java that prints only even numbers from 2 to 10 inclusive?

hard

A. for (int i = 0; i <= 10; i += 2) { System.out.print(i + " "); }

B. for (int i = 1; i < 10; i++) { if (i % 2 == 0) System.out.print(i + " "); }

C. for (int i = 2; i < 10; i++) { System.out.print(i * 2 + " "); }

D. for (int i = 2; i <= 10; i += 2) { System.out.print(i + " "); }

Solution

1. Step 1: Understand the requirement

   We want to print even numbers from 2 to 10 inclusive, so numbers: 2, 4, 6, 8, 10.

2. Step 2: Analyze each option

   for (int i = 2; i <= 10; i += 2) { System.out.print(i + " "); } starts at 2 and increments by 2 up to 10, printing even numbers correctly. for (int i = 1; i < 10; i++) { if (i % 2 == 0) System.out.print(i + " "); } uses a condition inside the loop but loops only up to 9, missing 10. for (int i = 2; i < 10; i++) { System.out.print(i * 2 + " "); } prints multiples of 2 starting at 4 (2*2), but loop ends before 10 and prints wrong numbers. for (int i = 0; i <= 10; i += 2) { System.out.print(i + " "); } starts at 0, which is not in the required range.

3. Final Answer:

   for (int i = 2; i <= 10; i += 2) { System.out.print(i + " "); } -> Option D

4. Quick Check:

   Increment by 2 from 2 to 10 = for (int i = 2; i <= 10; i += 2) { System.out.print(i + " "); } [OK]

Hint: Use i += 2 starting at 2 for even numbers [OK]

Common Mistakes:

• Starting loop at 0 instead of 2
• Using wrong loop condition
• Multiplying inside print instead of increment