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:
While Loop
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.
