Unit 3: Java Programming

Chapter 3: Control Structures - Conditionals and Loops

1. Flow of Control

By default, statements in a Java program execute sequentially from top to bottom. Control structures alter this sequential flow: 1. Selection (Decision Making): if, if-else, nested if, switch. 2. Iteration (Looping): for, while, do-while. 3. Jump Statements: break, continue, return.

2. Decision Making Statements

1. if-else and if-else-if Ladder

int marks = 85;

if (marks >= 90) {
    System.out.println("Grade: A+");
} else if (marks >= 80) {
    System.out.println("Grade: A");
} else if (marks >= 70) {
    System.out.println("Grade: B");
} else {
    System.out.println("Grade: C");
}

2. The switch Statement

Selects one of many code blocks to be executed based on matching an expression value. - Expression can be: byte, short, int, char, String, or enum. - break prevents "fall-through" into subsequent cases. - default executes if no case matches.

int day = 3;
String dayName;

switch (day) {
    case 1: dayName = "Monday"; break;
    case 2: dayName = "Tuesday"; break;
    case 3: dayName = "Wednesday"; break;
    case 4: dayName = "Thursday"; break;
    case 5: dayName = "Friday"; break;
    case 6: dayName = "Saturday"; break;
    case 7: dayName = "Sunday"; break;
    default: dayName = "Invalid Day Number"; break;
}
System.out.println(dayName);

3. Iteration / Looping Statements

1. The for Loop (Definite Loop)

Ideal when the number of iterations is known beforehand.

// Syntax: for (initialization; condition; update) { ... }
for (int i = 1; i <= 5; i++) {
    System.out.print(i + " ");
}
// Output: 1 2 3 4 5

2. The while Loop (Entry-Controlled Loop)

Condition is tested before entering the loop body. If condition is false initially, the loop body never executes.

int count = 1;
while (count <= 5) {
    System.out.print(count + " ");
    count++;
}

3. The do-while Loop (Exit-Controlled Loop)

Condition is evaluated after the loop body executes. - Key Guarantee: Guaranteed to execute at least once, even if the condition is false from the start.

int num = 10;
do {
    System.out.println("Executed at least once!");
} while (num < 5);

Loop Comparison Table

4. Jump Statements: break vs. continue

// Example demonstrating break and continue
for (int i = 1; i <= 5; i++) {
    if (i == 3) continue; // skips 3
    if (i == 5) break;    // terminates before printing 5
    System.out.print(i + " ");
}
// Output: 1 2 4

5. Board Exam Output Questions

1. What will be the output of the following Java snippet? java int x = 2; while (x < 10) { x += 3; } System.out.println(x);
2. Trace:
   • Start: $x = 2$ ($2 < 10 o x = 5$)
   • Iteration 2: $x = 5$ ($5 < 10 o x = 8$)
   • Iteration 3: $x = 8$ ($8 < 10 o x = 11$)
   • Iteration 4: $11 < 10$ is False $ o$ Loop terminates.
3. Output: 11