For loop syntax in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a basic for loop

What is the output of this Java code?

Java

public class Main {
    public static void main(String[] args) {
        for (int i = 0; i < 3; i++) {
            System.out.print(i + " ");
        }
    }
}

A 0 1 2 3

B 0 1 2

C 1 2 3

D 1 2 3 4

💡 Hint

Remember the loop runs while i is less than 3, starting from 0.

The loop starts at 0 and runs while i is less than 3, so it prints 0, 1, and 2 with spaces.

🧠 Conceptual

intermediate

Understanding for loop components

Which part of the for loop controls how many times the loop runs?

A The condition part

B The initialization part

C The update part

D The body of the loop

💡 Hint

Think about what decides if the loop continues or stops.

The condition part is checked before each iteration; if false, the loop stops.

❓ Predict Output

advanced

Output with multiple variables in for loop

What is the output of this Java code?

Java

public class Main {
    public static void main(String[] args) {
        for (int i = 0, j = 3; i < 3; i++, j--) {
            System.out.print(i + "-" + j + " ");
        }
    }
}

A 0-3 1-2 2-1

B 0-3 1-2 2-1 3-0

C 1-2 2-1 3-0

D 0-3 1-2 2-1 3-0 4--1

💡 Hint

Both i and j change each loop; watch their values carefully.

The loop runs 3 times with i from 0 to 2 and j from 3 down to 1, printing pairs.

🔧 Debug

advanced

Identify the error in this for loop

What error does this Java code produce?

Java

public class Main {
    public static void main(String[] args) {
        for int i = 0; i < 5; i++) {
            System.out.print(i);
        }
    }
}

A No error, code runs fine

B SyntaxError: Missing semicolon after initialization

C SyntaxError: Missing curly braces around loop body

D SyntaxError: Missing parentheses around for loop header

💡 Hint

Check the syntax of the for loop header carefully.

The for loop header must be enclosed in parentheses. Missing them causes a syntax error.

🚀 Application

expert

Number of iterations in nested for loops

How many times does the inner loop run in total when this code executes?

Java

public class Main {
    public static void main(String[] args) {
        int count = 0;
        for (int i = 1; i <= 4; i++) {
            for (int j = 1; j <= i; j++) {
                count++;
            }
        }
        System.out.println(count);
    }
}

A 16

B 8

C 10

D 12

💡 Hint

Count how many times the inner loop runs for each i from 1 to 4.

The inner loop runs 1 + 2 + 3 + 4 = 10 times in total.