Loop Constructs

for Loop

Syntax:

for (initialization; condition; update) {
    // statements
}

The initialization typically starts at 0. This structure is ideal when the number of iterations is known in advance.

while Loop

Syntax:

while (condition) {
    // statements
}

Unlike for, while only includes a condition check. Initialization and update must be handled separately before or with in the loop body.

do-while Loop

Syntax:

do {
    // statements
} while (condition);

This ensures the block executes at least once, even if the condition is false initially.

Increment and Decrement Operators

Consider ++variable (prefix) and variable++ (postfix):

• ++variable: Increments the value first, then returns the updated value. Used in expressions where the new value is needed immediately.

Example:

int num = 99;
int result = ++num; // result = 100, num = 100

• variable++: Returns the current value first, then increments it.

Example:

int num = 99;
int result = num++; // result = 99, num = 100

Decrement (--) follows the same logic.

Wrapper Classes

Java wraps primitive types into objects via wrapper classes to enable object-oriented operations. These classes provide utility methods and support generic collections.

Wrapping allows primitives to be used in contexts requiring objects.

Autoboxing and Unboxing

Automatic conversion between primitives and their wrapper classes:

• Autoboxing:

int age = 25;
Integer wrappedAge = age; // Automatically converted to Integer

• Unboxing:

Integer wrappedAge = 30;
int age = wrappedAge; // Extracted back to int

Type Conversion

• Implicit Casting: Smaller type values are automatically promoted to larger types during arithmetic operations.

• Explicit Casting: Forces a conversion from larger to smaller types using parentehses. May lead to precision loss.

Example:

int largeValue = 200;
byte smallValue = (byte) largeValue; // Truncates to fit byte range
System.out.println(smallValue); // Output: 200 (if no overflow)

Problem Statement

Calculate the sum of two integers a and b, but input format varies.

Input Format

• First line: an integer N, indicating the number of test cases.
• Next N lines: each contains two integers a and b separated by a space.

Output Format

• For each pair (a, b), print a + b on a separate line.

Solution Using for Loop

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int count = scanner.nextInt();
        for (int i = 0; i < count; i++) {
            int a = scanner.nextInt();
            int b = scanner.nextInt();
            System.out.println(a + b);
        }
        scanner.close();
    }
}

Solution Using while Loop

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        while (n > 0) {
            int a = scanner.nextInt();
            int b = scanner.nextInt();
            System.out.println(a + b);
            n--;
        }
        scanner.close();
    }
}