Conditional Statements

In C, conditional statements are the backbone of decision-making in your programs. They allow you to control the flow of execution based on specific conditions. This section dives deep into two essential conditional structures: if / else and switch. By mastering these, you’ll be able to build programs that respond intelligently to varying inputs and scenarios.

If / Else Statements

The if / else statement is the simplest and most fundamental conditional structure in C. It lets you execute a block of code if a condition is true, and an alternative block if the condition is false. This construct is your go-to for basic decision logic.

Syntax and Structure

The basic syntax is:

<code class="language-c">if (condition) {
<p>    // Code to run if condition is true</p>
<p>} else {</p>
<p>    // Code to run if condition is false</p>
<p>}</code>

You can also chain multiple conditions using else if:

<code class="language-c">if (condition1) {
<p>    // Code block 1</p>
<p>} else if (condition2) {</p>
<p>    // Code block 2</p>
<p>} else {</p>
<p>    // Code block 3 (if none of the above conditions are true)</p>
<p>}</code>

Practical Examples

Example 1: Checking for Even or Odd Numbers

<code class="language-c">#include <stdio.h>

<p>int main() {</p>
<p>    int number = 7;</p>
<p>    if (number % 2 == 0) {</p>
<p>        printf("The number is even.\n");</p>
<p>    } else {</p>
<p>        printf("The number is odd.\n");</p>
<p>    }</p>
<p>    return 0;</p>
<p>}</code>

Output when number = 7: The number is odd.

Example 2: Grade Determination

<code class="language-c">#include <stdio.h>

<p>int main() {</p>
<p>    int score = 85;</p>
<p>    if (score >= 90) {</p>
<p>        printf("Grade: A\n");</p>
<p>    } else if (score >= 80) {</p>
<p>        printf("Grade: B\n");</p>
<p>    } else if (score >= 70) {</p>
<p>        printf("Grade: C\n");</p>
<p>    } else {</p>
<p>        printf("Grade: F\n");</p>
<p>    }</p>
<p>    return 0;</p>
<p>}</code>

Output when score = 85: Grade: B

Example 3: Simple User Input Validation

<code class="language-c">#include <stdio.h>

<p>int main() {</p>
<p>    int age;</p>
<p>    printf("Enter your age: ");</p>
<p>    scanf("%d", &age);</p>

<p>    if (age < 0) {</p>
<p>        printf("Error: Age cannot be negative.\n");</p>
<p>    } else {</p>
<p>        printf("Your age is: %d\n", age);</p>
<p>    }</p>
<p>    return 0;</p>
<p>}</code>

This program validates user input for age, ensuring it’s non-negative.

Key Points to Remember

Always use braces {} for code blocks to avoid ambiguity (especially when adding more conditions later).
Condition expressions must evaluate to true/false. In C, non-zero values are true, and zero is false.
The else block is optional if you don’t need to handle the false case (though it’s common practice to include it for clarity).

Switch Statements

The switch statement provides a more readable alternative to multiple if / else statements when dealing with multiple discrete values. It’s particularly useful for handling integer or character-based options efficiently.

Syntax and Structure

The syntax for a switch statement is:

<code class="language-c">switch (expression) {
<p>    case constant1:</p>
<p>        // Code block for constant1</p>
<p>        break;</p>
<p>    case constant2:</p>
<p>        // Code block for constant2</p>
<p>        break;</p>
<p>    ...</p>
<p>    default:</p>
<p>        // Code block for unmatched values</p>
<p>}</code>

The expression is evaluated once.
The value is compared to each case label.
When a match is found, the corresponding block executes, and break exits the switch (preventing “fall-through” to subsequent cases).

Practical Examples

Example 1: Simple Menu Selection

<code class="language-c">#include <stdio.h>

<p>int main() {</p>
<p>    int choice;</p>
<p>    printf("Choose a number (1-3): ");</p>
<p>    scanf("%d", &choice);</p>

<p>    switch (choice) {</p>
<p>        case 1:</p>
<p>            printf("You chose 1.\n");</p>
<p>            break;</p>
<p>        case 2:</p>
<p>            printf("You chose 2.\n");</p>
<p>            break;</p>
<p>        case 3:</p>
<p>            printf("You chose 3.\n");</p>
<p>            break;</p>
<p>        default:</p>
<p>            printf("Invalid choice.\n");</p>
<p>    }</p>
<p>    return 0;</p>
<p>}</code>

Output when choice = 2: You chose 2.

Example 2: Handling Character Grades

<code class="language-c">#include <stdio.h>

<p>int main() {</p>
<p>    char grade = 'B';</p>
<p>    switch (grade) {</p>
<p>        case 'A':</p>
<p>            printf("Grade: A\n");</p>
<p>            break;</p>
<p>        case 'B':</p>
<p>            printf("Grade: B\n");</p>
<p>            break;</p>
<p>        case 'C':</p>
<p>            printf("Grade: C\n");</p>
<p>            break;</p>
<p>        default:</p>
<p>            printf("Unknown grade.\n");</p>
<p>    }</p>
<p>    return 0;</p>
<p>}</code>

Output when grade = 'B': Grade: B

Example 3: Using switch with Integers

<code class="language-c">#include <stdio.h>

<p>int main() {</p>
<p>    int day = 3;</p>
<p>    switch (day) {</p>
<p>        case 1:</p>
<p>            printf("Monday\n");</p>
<p>            break;</p>
<p>        case 2:</p>
<p>            printf("Tuesday\n");</p>
<p>            break;</p>
<p>        case 3:</p>
<p>            printf("Wednesday\n");</p>
<p>            break;</p>
<p>        default:</p>
<p>            printf("Invalid day.\n");</p>
<p>    }</p>
<p>    return 0;</p>
<p>}</code>

Output when day = 3: Wednesday

Key Points to Remember

Each case must have a break statement (or return) to prevent “fall-through” (i.e., the program continuing to execute the next case).
The default case is optional and executes when no case matches the expression.
Use switch for discrete values (e.g., integers, characters) but avoid it for ranges or complex conditions.

When to Use Switch vs If-Else

Here’s a comparison table to help you decide:

Scenario	Use `if-else`	Use `switch`
Multiple discrete integer values	❌ (less readable)	✅ (more readable and concise)
Range checks (e.g., `x > 5`)	✅ (natural)	❌ (not suitable)
Character or string comparisons	✅ (with `strcmp` for strings)	✅ (for single characters)
Complex conditions	✅ (e.g., nested conditions)	❌ (not designed for this)

Note: For strings, switch is not directly supported (use if with strcmp or strcmp in the condition).

Summary

In this section, we’ve covered two essential conditional structures in C: if / else and switch.

The if / else statements are your go-to for simple and compound conditions, allowing precise control over program flow based on boolean expressions.
The switch statement excels at handling multiple discrete values efficiently, making your code more readable when dealing with a set of fixed options.

Both constructs are foundational for writing robust and maintainable C programs. Remember to:

Use braces {} for code blocks.
Always include break in switch cases to avoid fall-through.
Choose if / else for complex logic and switch for discrete value handling.

By mastering these concepts, you’ll be able to build decision-driven logic that responds confidently to your program’s needs. 💡