Control Flow

This document covers Control Flow in C.

Control flow determines the order in which statements are executed in a C program. C provides several control flow structures, including conditional statements and loops, to control the execution of code based on conditions or repetitions.

Conditional Statements

Conditional statements allow a program to make decisions and execute different code blocks based on conditions.

if-else Statement

The if statement executes a block of code only if a condition is true. The else statement executes if the if condition is false. If there a multiple conditions to be checked, then else-if can be used.

Example

#include <stdio.h>
int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);

    if (num > 0) {
        printf("The number is positive.\n");
    } else if (num < 0) {
        printf("The number is negative.\n");
    } else {
        printf("The number is zero.\n");
    }
    return 0;
}

info

The program checks if the number is positive, negative, or zero.

Switch Case Statement

The switch statement is used to evaluate a single expression and execute different blocks of code based on its value. Each case must end with a break; statement to prevent fall-through.

Example

#include <stdio.h>
int main() {
    int day;
    printf("Enter a number (1-7) for a day of the week: ");
    scanf("%d", &day);

    switch (day) {
        case 1: printf("Monday\n"); break;
        case 2: printf("Tuesday\n"); break;
        case 3: printf("Wednesday\n"); break;
        case 4: printf("Thursday\n"); break;
        case 5: printf("Friday\n"); break;
        case 6: printf("Saturday\n"); break;
        case 7: printf("Sunday\n"); break;
        default: printf("Invalid input!\n");
    }
    return 0;
}

info

The program takes an integer input (1-7) and prints the corresponding weekday.

Loops in C

Loops allow repeating a block of code multiple times until a condition is met.

For Loop

The for loop is used when the number of iterations is known beforehand.

Example

#include <stdio.h>
int main() {
    for (int i = 1; i <= 5; i++) {
        printf("Iteration %d\n", i);
    }
    return 0;
}

info

The loop runs 5 times, printing the iteration number each time.

While Loop

The while loop executes as long as the condition remains true.

Example:

#include <stdio.h>
int main() {
    int count = 1;
    while (count <= 5) {
        printf("Count: %d\n", count);
        count++;
    }
    return 0;
}

info

The loop increments count until it reaches 5.

Do-While Loop

The do-while loop guarantees at least one execution before checking the condition.

Example:

#include <stdio.h>
int main() {
    int num;
    do {
        printf("Enter a positive number: ");
        scanf("%d", &num);
    } while (num <= 0);

    printf("You entered: %d\n", num);
    return 0;
}

info

This loop ensures the user must enter a positive number before proceeding.

Break and Continue Statements

• The break statement is used to exit a loop prematurely when a condition is met.

• The continue statement skips the rest of the current iteration and moves to the next.

Example using break

#include <stdio.h>
int main() {
    for (int i = 1; i <= 10; i++) {
        if (i == 5) {
            break; // Stops the loop when i reaches 5
        }
        printf("%d ", i);
    }
    return 0;
}

Example using continue

#include <stdio.h>
int main() {
    for (int i = 1; i <= 10; i++) {
        if (i == 5) {
            continue; // Skips printing 5
        }
        printf("%d ", i);
    }
    return 0;
}

info

• break stops the loop completely when i == 5.

• continue skips i == 5 but continues the loop.