Control Flow and Loops

35 min

Control flow structures determine the order in which program statements execute. C provides conditional statements (if, else, switch) for decision-making and loops (while, do-while, for) for repetition. Understanding control flow is fundamental to programming, as it enables programs to make decisions and repeat operations. Control flow structures can be nested to create complex program logic.

If-else statements enable conditional execution based on boolean expressions. If the condition is true, the if block executes; otherwise, the else block (if present) executes. If-else chains (else if) enable multiple conditions. Conditions use relational and logical operators to evaluate to true (non-zero) or false (zero). Understanding if-else enables decision-making in programs.

Switch statements provide multi-way branching based on integer or character values. Switch compares a value against multiple case labels and executes the matching case. The break statement exits the switch, preventing fall-through to subsequent cases. The default case handles unmatched values. Understanding switch enables efficient multi-way decisions.

While loops repeat code while a condition is true. The condition is evaluated before each iteration, so the loop may execute zero or more times. While loops are ideal when the number of iterations is unknown beforehand. Understanding while loops enables repetition based on conditions.

For loops provide compact syntax for loops with initialization, condition, and increment. For loops are ideal when you know the number of iterations or need to iterate over a range. The for loop syntax combines initialization, condition checking, and increment in one statement. Understanding for loops enables efficient iteration.

Do-while loops are similar to while loops but evaluate the condition after each iteration, ensuring at least one execution. Break exits loops immediately, while continue skips to the next iteration. Nested control structures enable complex logic. Understanding all loop types enables choosing the appropriate loop for each situation.

Key Concepts

Control flow structures determine statement execution order.
If-else statements enable conditional execution.
Switch statements provide multi-way branching.
Loops (while, do-while, for) enable repetition.
Break and continue control loop execution.

Learning Objectives

Master

Using if-else statements for conditional execution
Implementing switch statements for multi-way decisions
Creating while, do-while, and for loops
Using break and continue in loops

Develop

Understanding program flow and logic
Designing efficient control structures
Implementing complex program logic

Tips

Use if-else for binary decisions: if (condition) { ... } else { ... }.
Use switch for multiple values: switch (value) { case 1: ... break; }.
Use for loops for known iterations: for (int i = 0; i < n; i++) { ... }.
Use break to exit loops: break; exits the innermost loop.

Common Pitfalls

Forgetting break in switch, causing fall-through to next case.
Creating infinite loops, causing programs to hang.
Using wrong loop type, making code less readable or efficient.
Not understanding loop conditions, causing off-by-one errors.

Summary

Control flow structures enable decision-making and repetition.
If-else and switch provide conditional execution.
Loops enable repeating code efficiently.
Understanding control flow is fundamental to programming.

Exercise

Create programs demonstrating different control flow structures.

#include <stdio.h>

int main() {
    int score = 85;
    
    // If-else ladder
    if (score >= 90) {
        printf("Grade: A
");
    } else if (score >= 80) {
        printf("Grade: B
");
    } else if (score >= 70) {
        printf("Grade: C
");
    } else {
        printf("Grade: D
");
    }
    
    // Switch statement
    int day = 3;
    switch (day) {
        case 1:
            printf("Monday
");
            break;
        case 2:
            printf("Tuesday
");
            break;
        case 3:
            printf("Wednesday
");
            break;
        default:
            printf("Other day
");
    }
    
    // For loop
    printf("Counting from 1 to 5:
");
    for (int i = 1; i <= 5; i++) {
        printf("%d ", i);
    }
    printf("
");
    
    // While loop
    printf("Counting down from 5:
");
    int count = 5;
    while (count > 0) {
        printf("%d ", count);
        count--;
    }
    printf("
");
    
    // Do-while loop
    printf("Do-while example:
");
    int num = 1;
    do {
        printf("%d ", num);
        num++;
    } while (num <= 3);
    printf("
");
    
    return 0;
}

Exercise Tips

Use continue to skip iterations: continue; jumps to next loop iteration.
Nest loops carefully: for (int i = 0; i < n; i++) { for (int j = 0; j < m; j++) { ... } }.
Use break in switch: always include break; to prevent fall-through.
Validate loop conditions: ensure loops terminate to avoid infinite loops.

Control Flow and Loops