PPL UNIT 3 2024-25

Control Structures and Loops in C

Overview of Control Structures

Control structures are essential in programming as they guide the flow of execution based on conditions.
The primary control structures in C include:
- Selection Statements: Determine the flow based on conditions (e.g., if, switch).
- Iterative Statements: Execute blocks of code multiple times (e.g., for, while, do while).
- Unconditional Branching: Jumps to specific parts of code (e.g., break, continue, goto).
- Guarded Commands: Conditional statements that guard the execution of their attached commands.

Selection Statements

Definition: A method for executing different parts of code based on the evaluation of conditions.
Types of Selection Statements:
- If Statement: Executes a block if a condition is true.
  - Syntax: if (condition) { // statements }
- If-Else Statement: Executes one block if the condition is true, or another if false.
- If-Else-If Ladder: Allows checking multiple conditions in a sequential manner.
- Switch Statement: Selects a block to execute based on the value of an expression.
Example of If-Else Statement:
- "If x > y, execute block A; else, execute block B."

Nested Conditional Statements

Nested if: An if statement within another if statement, useful for checking multiple conditions.
- Example: Checking if a number is valid while also checking if it meets certain criteria.

Iterative Statements (Loops)

Purpose: To repeat a statement or block of statements until a specified condition is met.
Types of Loops:
- While Loop: Checks the condition before executing the block; entry-controlled.
  - Syntax:
```
while (condition) {
    // statements
}
```
- Do-While Loop: Executes the block first and then checks the condition; exit-controlled.
  - Syntax:
```
do {
    // statements
} while (condition);
```
- For Loop: Designed for a known number of iterations, initializes a counter, checks a condition, and updates the counter in a single line.
  - Syntax:
```
for (initialization; condition; increment) {
    // statements
}
```

Control Flow Modifications

Break: Exits from loops or switch cases prematurely.
Continue: Skips the current iteration of a loop and jumps to the next iteration.
Goto: Provides a way to jump to different parts in the code using labels.

Examples of Control Structures in C

If Statement Example:

if (i > 15) {
    printf("%d is greater than 15", i);
}

If-Else Example:

if (i < 15) {
    printf("%d is smaller than 15", i);
} else {
    printf("%d is greater than 15", i);
}

Switch Statement Example:

switch (var) {
    case 1:
        printf("Case 1 is executed");
        break;
    case 2:
        printf("Case 2 is executed");
        break;
    default:
        printf("Default Case is executed");
        break;
}

While Loop Example:

int i = 1;
while (i <= 10) {
    printf("%d", i);
    i++;
}

For Loop Example:

for (int j = 0; j < 10; j++) {
    printf("%d", j);
}

Conclusion

Control structures are foundational in C programming, allowing for decision making and repetition. Understanding how to effectively use if, switch, and looping constructs such as for, while, and do-while is crucial for creating efficient programs. By mastering these concepts, programmers can control the flow of execution in a logical and structured manner.