Part 3: Control Flow: If-Else, Loops in C

Welcome back to Part 3 of our "Getting Started with C" series! In the previous parts, we laid the groundwork by understanding the basics of C and how to work with variables, data types, and operators. Now, we're going to learn how to make our programs more intelligent and versatile by introducing control flow statements. These statements allow you to execute different blocks of code based on certain conditions or to repeat a block of code multiple times.

Conditional Statements: Making Decisions with if, else if, and else

Conditional statements allow your program to make decisions and execute different paths of code based on whether a certain condition is true or false. The most common conditional statement in C is the if statement.

The if Statement

The if statement executes a block of code only if a specified condition is true. The syntax is as follows:

if (condition) {
    // Code to be executed if the condition is true
}

The condition is an expression that evaluates to either true (non-zero) or false (zero). If the condition is true, the code inside the curly braces {} is executed.

Example:

#include <stdio.h>

int main() {
    int age = 20;

    if (age >= 18) {
        printf("You are eligible to vote.\n");
    }

    return 0;
}

In this example, the message "You are eligible to vote." will be printed only if the value of the age variable is 18 or greater.

The else Statement

The else statement can be used in conjunction with an if statement to execute a block of code if the condition in the if statement is false. The syntax is:

if (condition) {
    // Code to be executed if the condition is true
} else {
    // Code to be executed if the condition is false
}

Example:

#include <stdio.h>

int main() {
    int age = 15;

    if (age >= 18) {
        printf("You are eligible to vote.\n");
    } else {
        printf("You are not yet eligible to vote.\n");
    }

    return 0;
}

In this case, since age is 15 (less than 18), the message "You are not yet eligible to vote." will be printed.

The else if Statement

Sometimes, you might have multiple conditions to check. The else if statement allows you to check additional conditions if the preceding if or else if conditions were false. The syntax is:

if (condition1) {
    // Code to be executed if condition1 is true
} else if (condition2) {
    // Code to be executed if condition1 is false AND condition2 is true
} else if (condition3) {
    // Code to be executed if condition1 and condition2 are false AND condition3 is true
} else {
    // Code to be executed if none of the above conditions are true
}

You can have multiple else if statements. The else block at the end is optional and will be executed if none of the preceding conditions are true.

Example:

#include <stdio.h>

int main() {
    int score = 75;

    if (score >= 90) {
        printf("Grade: A\n");
    } else if (score >= 80) {
        printf("Grade: B\n");
    } else if (score >= 70) {
        printf("Grade: C\n");
    } else if (score >= 60) {
        printf("Grade: D\n");
    } else {
        printf("Grade: F\n");
    }

    return 0;
}

In this example, the program will determine and print the corresponding letter grade based on the value of the score variable.

Looping Structures: Repeating Actions with for, while, and do-while

Loops allow you to execute a block of code repeatedly until a certain condition is met. C provides three main types of loops: for, while, and do-while.

The for Loop

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

for (initialization; condition; increment/decrement) {
    // Code to be executed repeatedly
}

• Initialization: This statement is executed only once at the beginning of the loop. It's often used to initialize a loop counter variable.
• Condition: This expression is evaluated before each iteration of the loop. If the condition is true, the loop body is executed. If it's false, the loop terminates.
• Increment/Decrement: This statement is executed at the end of each iteration. It's often used to update the loop counter.

Example:

#include <stdio.h>

int main() {
    for (int i = 1; i <= 5; i++) {
        printf("The value of i is: %d\n", i);
    }

    return 0;
}

This loop will print the message "The value of i is: [number]" five times, with the value of i ranging from 1 to 5.

The while Loop

The while loop executes a block of code as long as a specified condition is true. The condition is checked before each iteration. The syntax is:

while (condition) {
    // Code to be executed as long as the condition is true
}

Example:

#include <stdio.h>

int main() {
    int count = 0;

    while (count < 3) {
        printf("Count is: %d\n", count);
        count++; // Increment the counter to eventually make the condition false
    }

    return 0;
}

This loop will print the value of count (0, 1, and 2) as long as count is less than 3. It's crucial to ensure that the condition eventually becomes false to avoid an infinite loop.

The do-while Loop

The do-while loop is similar to the while loop, but it guarantees that the loop body will be executed at least once because the condition is checked after the first iteration. The syntax is:

do {
    // Code to be executed at least once, and then repeatedly as long as the condition is true
} while (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;
}

This loop will keep prompting the user to enter a positive number until a positive number is entered.

Controlling Loop Execution: break and continue

C provides two special statements that can be used to alter the normal flow of execution within loops:

• break: The break statement immediately terminates the innermost enclosing loop (or switch statement). The program execution continues with the statement immediately following the loop.
• continue: The continue statement skips the rest of the current iteration of the loop and proceeds to the next iteration.

We'll explore these statements in more detail in future parts of the series when we encounter scenarios where they are particularly useful.

What's Next?

In the next part of our "Getting Started with C" series, we will dive into the world of functions in C. You'll learn how to define your own functions to create reusable blocks of code and make your programs more organized and manageable. Stay tuned!

Suggestions:

• If you want to review the different types of operators we discussed in the previous part, you can find that information here: "Variables, Data Types, and Operators in C".
• Understanding boolean logic is crucial for working with conditional statements. You might find our explanation of "[Boolean Logic in Programming]" helpful.
• As we briefly mentioned the switch statement, you might want to explore its usage in our article on "[The Switch Statement in C]".
• For a more advanced understanding of loop control, you can look forward to our future content on "[Link to a potential future blog post about Advanced Loop Techniques in C]".

This content thoroughly covers control flow in C for beginners, providing a strong understanding of how to make programs make decisions and repeat actions.

Topic covered in this article:

• Control Flow

• If-Else

• Loops

• For Loop

• While Loop

• Do-While Loop