Control Flow Statements in Java

On Day 3, we will focus on understanding how Java programs make decisions and control the flow of execution based on different conditions and loops.

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1. Introduction to Control Flow

Control flow refers to the order in which individual statements, instructions, or function calls are executed or evaluated in a program. In Java, control flow can be managed using conditional statements and loops.

• Conditional Statements allow the program to execute a block of code if a particular condition is true.

• Loops allow repeated execution of a block of code as long as a certain condition is met.

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2. if, if-else, and else-if Statements

The if-else statement is one of the most commonly used conditional control flow structures. It checks a condition and executes a block of code if the condition is true, and an alternative block if the condition is false.

Basic if Statement:

int number = 10;

if (number > 5) {
    System.out.println("Number is greater than 5");
}

if-else Statement:

int number = 4;

if (number > 5) {
    System.out.println("Number is greater than 5");
} else {
    System.out.println("Number is not greater than 5");
}

else-if Ladder: This structure is used when you need to test multiple conditions.

int score = 85;

if (score >= 90) {
    System.out.println("Grade: A");
} else if (score >= 80) {
    System.out.println("Grade: B");
} else if (score >= 70) {
    System.out.println("Grade: C");
} else {
    System.out.println("Grade: D or lower");
}

Points to Remember:

• The condition in the if statement must be a boolean expression, i.e., it should evaluate to true or false.

• You can have multiple else-if statements, but only one else block.

• Once a condition is true, no further conditions in the else-if ladder are checked.

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3. The switch Statement

The switch statement is used when you have multiple possible values for a variable, and you want to execute different code blocks depending on the value. It's an alternative to using multiple else-if statements when comparing the same variable.

Syntax:

int day = 3;

switch (day) {
    case 1:
        System.out.println("Sunday");
        break;
    case 2:
        System.out.println("Monday");
        break;
    case 3:
        System.out.println("Tuesday");
        break;
    default:
        System.out.println("Invalid day");
}

Enhanced Switch Case Syntax :

int day = 3;

switch(day){
      // here no need to specify break statement
      case 1 -> System.out.println("Monday");
      case 2 -> System.out.println("Tuesday");
      case 3 -> System.out.println("Wednesday");
      case 4 -> System.out.println("Thrusday");
      case 5 -> System.out.println("Friday");
      case 6 -> System.out.println("Saturday");
      case 7 -> System.out.println("Sunday");
      default -> System.out.println("Invalid Number of Day..");
   }

Key Points:

• Each case block compares the variable (day) with a constant value.

• The break statement exits the switch block once a matching case is executed. Without break, execution would continue to the next case.

• The default case is optional and executes if none of the cases match.

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4. Loops in Java

Loops are used to repeatedly execute a block of code as long as the loop's condition remains true. Java provides three types of loops: for loop, while loop, and do-while loop.

for Loop: The for loop is used when you know in advance how many times you want to repeat a block of code.

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

for-each Loop:

int ar[] = { 10, 50, 60, 80, 90 }; 
for (int element : ar) 
     System.out.print(element + " "); 
}

• The loop consists of three parts: initialization, condition, and increment/decrement.

• In the example, i starts at 0, and the loop continues as long as i < 5. After each iteration, i is incremented by 1.

while Loop: The while loop executes as long as a given condition is true. It's used when the number of iterations is not known beforehand.

int i = 0;

while (i < 5) {
    System.out.println("i: " + i);
    i++;
}

• Here, the loop checks the condition before executing the block of code. If the condition is false at the beginning, the loop won’t run even once.

do-while Loop: The do-while loop is similar to the while loop but guarantees that the code block is executed at least once, even if the condition is false initially.

int i = 0;

do {
    System.out.println("i: " + i);
    i++;
} while (i < 5);

Key Differences Between Loops:

• for loop: Used when the number of iterations is known.

• while loop: Used when the condition needs to be checked before each iteration.

• do-while loop: Used when the block of code needs to be executed at least once.

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5. Break and Continue Statements

• break: Exits the loop or switch statement immediately.

• continue: Skips the current iteration of the loop and moves to the next iteration.

Example of break:

for (int i = 0; i < 10; i++) {
    if (i == 5) {
        break;  // Exit the loop when i is 5
    }
    System.out.println("i: " + i);
}

Example of continue:

for (int i = 0; i < 10; i++) {
    if (i == 5) {
        continue;  // Skip the iteration when i is 5
    }
    System.out.println("i: " + i);
}

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6. Nested Loops

A loop inside another loop is called a nested loop. They are often used in scenarios like printing patterns or handling multidimensional arrays.

Example of a Nested Loop:

for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 3; j++) {
        System.out.println("i: " + i + ", j: " + j);
    }
}

Output:

i: 1, j: 1
i: 1, j: 2
i: 1, j: 3
i: 2, j: 1
i: 2, j: 2
i: 2, j: 3
i: 3, j: 1
i: 3, j: 2
i: 3, j: 3

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7. Practical Example: Number Guessing Game

Here's a small practical project that uses control flow and loops to create a number guessing game:

import java.util.Scanner;

public class GuessingGame {
    public static void main(String[] args) {
        int targetNumber = (int) (Math.random() * 100) + 1;  // Generate a random number between 1 and 100  
        Scanner scanner = new Scanner(System.in);
        int guess;
        int attempts = 0;

        do {
            System.out.print("Guess a number between 1 and 100: ");
            guess = scanner.nextInt();
            attempts++;

            if (guess > targetNumber) {
                System.out.println("Too high!");
            } else if (guess < targetNumber) {
                System.out.println("Too low!");
            } else {
                System.out.println("Correct! You guessed it in " + attempts + " attempts.");
            }
        } while (guess != targetNumber);

        scanner.close();
    }
}

How it Works:

• The game generates a random number between 1 and 100.

• The player guesses the number, and the program provides feedback (Too high or Too low) until the player guesses correctly.

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Summary of Day 4

By the end of Day 3, we will have a solid understanding of:

• Conditional statements like if, if-else, and switch.

• Different types of loops (for, while, do-while) and their use cases.

• The purpose and use of break and continue.

• Practical applications of control flow in Java.

This knowledge will equip readers with the skills to write more dynamic, interactive programs that can make decisions and handle repetitive tasks effectively. So stay tuned!! for more advanced topics.