Conditional Statements and Loops
If-Else Statement
Used to check Boolean conditions (True or False).
Syntax:
if (boolean expression){ // Body } else { // Do this }Example:
public class IfElse { public static void main(String[] args) { int salary = 25400; if (salary > 10000) { salary = salary + 2000; } else { salary = salary + 1000; } System.out.println(salary); } }Output: 27400
Multiple If-Else Statement
Executes one condition from multiple statements.
Syntax:
if (condition1) { // Code to be executed if condition1 is true } else if (condition2) { // Code to be executed if condition2 is true } else if (condition3) { // Code to be executed if condition3 is true } else { // Code to be executed if all conditions are false }Example:
public class MultipleIfElse { public static void main(String[] args) { int salary = 25400; if (salary <= 10000) { salary += 1000; } else if (salary <= 20000) { salary += 2000; } else { salary += 3000; } System.out.println(salary); } }Output: 28400
Loops
For Loop:
Used when the number of iterations is known.
Syntax:
for (initialization; condition; increment/decrement){ // Body }Example 1:
public class ForLoop { public static void main(String[] args) { for (int num = 1; num <= 5; num += 1){ System.out.println(num); } } }Output: 1, 2, 3, 4, 5
Example 2:
import java.util.Scanner; public class ForLoop { public static void main(String[] args) { Scanner in = new Scanner(System.in); int n = in.nextInt(); for (int num = 1; num <= n; num += 1){ System.out.print(num + " "); } } }Input: 6
Output: 1 2 3 4 5 6
While Loop:
Used when the number of iterations is not known.
Syntax:
while (condition){ // Code to be executed // Increment/Decrement }Example:
public class WhileLoop { public static void main(String[] args) { int num = 1; while (num <= 5){ System.out.println(num); num += 1; } } }Output: 1, 2, 3, 4, 5
Do-While Loop:
Used when the loop needs to execute at least once.
Exit-controlled loop.
Syntax:
do { // Code to be executed // Update statement (increment/decrement) } while (condition);Example:
public class DoWhileLoop { public static void main(String[] args) { int n = 1; do { System.out.println(n); n++; } while (n <= 5); } }Output: 1, 2, 3, 4, 5
Comparison between While Loop and Do-While Loop:
Used when the number of iterations is not fixed
Used when we want to execute the statement at least once
Entry-controlled loop
Exit-controlled loop
No semicolon required at the end of while (condition)
Semicolon is required at the end of while (condition)
Programs
🎯 Program: Largest of Three Numbers
Problem Statement: "Find largest among three numbers."
Approach 1:
import java.util.Scanner; public class LargestOfThree { public static void main(String[] args) { Scanner in = new Scanner(System.in); int a = in.nextInt(); int b = in.nextInt(); int c = in.nextInt(); int max = a; if (b > max) { max = b; } if (c > max) { max = c; } System.out.println(max); } }Approach 2:
import java.util.Scanner; public class LargestOfThree { public static void main(String[] args) { Scanner in = new Scanner(System.in); int a = in.nextInt(); int b = in.nextInt(); int c = in.nextInt(); int max = 0; if (a > b) { max = a; } else { max = b; } if (c > max) { max = c; } System.out.println(max); } }Approach 3 (Using
Math.max):import java.util.Scanner; public class LargestOfThree { public static void main(String[] args) { Scanner in = new Scanner(System.in); int a = in.nextInt(); int b = in.nextInt(); int c = in.nextInt(); int max = Math.max(c, Math.max(a, b)); System.out.println(max); } }Input: 3 6 5
Output: 6
🎯 Program: Alphabet Case Check
Problem Statement: "Take an input character from the keyboard and check whether it is an uppercase alphabet or lowercase alphabet."
Example:
import java.util.Scanner; public class AlphabetCaseCheck { public static void main(String[] args) { Scanner in = new Scanner(System.in); char ch = in.next().trim().charAt(0); if (ch >= 'a' && ch <= 'z') { System.out.println("Lowercase"); } else { System.out.println("Uppercase"); } } }Input: a
Output: Lowercase
Input: Z
Output: Uppercase
🎯 Program: Fibonacci Numbers
Problem Statement: "Find the nth Fibonacci number."
Example:
import java.util.Scanner; public class FibonacciNumbers { public static void main(String[] args) { Scanner in = new Scanner(System.in); int n = in.nextInt(); int a = 0, b = 1, count = 2; while (count <= n) { int temp = b; b = b + a; a = temp; count++; } System.out.println(b); } }Input: 7
Output: 13
🎯 Program: Counting Occurrence
Problem Statement: "Input two numbers, find how many times the second number's digit is present in the first number."
Example:
import java.util.Scanner; public class CountingOccurrence { public static void main(String[] args) { Scanner in = new Scanner(System.in); int count = 0; int Fn = in.nextInt(); int Sn = in.nextInt(); while (Fn > 0) { int rem = Fn % 10; if (rem == Sn) { count++; } Fn = Fn / 10; } System.out.println(count); } }Input: 45535 5
Output: 3
🎯 Program: Reverse a Number
Problem Statement: "Input a number from the keyboard and show the output as the reverse of that number."
Example:
import java.util.Scanner; public class ReverseANumber { public static void main(String[] args) { Scanner in = new Scanner(System.in); int num = in.nextInt(); int reversedNum = 0; while (num > 0) { int rem = num % 10; num /= 10; reversedNum = reversedNum * 10 + rem; } System.out.println(reversedNum); } }Input: 458792
Output: 297854
🎯 Program: Calculator Program
Example of a simple calculator program.
Input and output are managed until the user presses 'X' or 'x'.
import java.util.Scanner; public class Calculator { public static void main(String[] args) { Scanner in = new Scanner(System.in); int ans = 0; while (true) { System.out.print("Enter the operator: "); char op = in.next().trim().charAt(0); if (op == '+' || op == '-' || op == '*' || op == '/' || op == '%') { System.out.print("Enter two numbers: "); int num1 = in.nextInt(); int num2 = in.nextInt(); switch (op) { case '+': ans = num1 + num2; break; case '-': ans = num1 - num2; break; case '*': ans = num1 * num2; break; case '/': if (num2 != 0) { ans = num1 / num2; } break; case '%': ans = num1 % num2; break; } } else if (op == 'x' || op == 'X') { break; } else { System.out.println("Invalid operation!!"); } System.out.println(ans); } } }
Conclusion
To wrap up, diving into Conditional Statements and Loops equips you with essential tools for effective programming. The covered topics, from basic If-Else statements to versatile loops, offer practical solutions for various scenarios. The hands-on examples, like finding the largest number or building a basic calculator, reinforce your skills and prepare you for real-world coding challenges. In a nutshell, this learning journey sets a strong foundation for making informed decisions and handling repetitive tasks in Java programming.
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