🧠 C if…else Statements – Syntax, Nesting, and Examples

🧲 Introduction – What Are if...else Statements in C?

The if...else statement in C is a fundamental control structure used to execute different blocks of code based on a condition. It allows the program to make decisions dynamically during runtime, enabling conditional logic for real-world scenarios like login checks, value comparisons, and branching computations.

🎯 In this guide, you’ll learn:

• The syntax of if, else if, and else
• How conditional branching works
• Nested and compound conditions
• Best practices and common pitfalls

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🔹 Syntax of if...else

if (condition) {
    // Code runs if condition is true
} else {
    // Code runs if condition is false
}

🔹 With else if:

if (condition1) {
    // Executes if condition1 is true
} else if (condition2) {
    // Executes if condition2 is true
} else {
    // Executes if none are true
}

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🧪 Example: Basic if...else

int num = 10;

if (num > 0) {
    printf("Positive number");
} else {
    printf("Not positive");
}

Output:

Positive number

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🧠 Nested if...else Statements

You can nest one if...else inside another to check multiple layers of conditions.

if (score >= 50) {
    if (score >= 90) {
        printf("Excellent");
    } else {
        printf("Passed");
    }
} else {
    printf("Failed");
}

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🔁 Compound Conditions with Logical Operators

You can combine multiple conditions using logical operators &&, ||, and !.

if (age > 18 && age < 60) {
    printf("Eligible to work");
}

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⚠️ Common Pitfalls

Mistake	Issue
Using = instead of ==	Assignment instead of comparison
Forgetting braces {} for multiple lines	May lead to logical bugs
Not covering all paths with else	May leave code undefined under some conditions

✅ Good Practice:

if (x == 5) {
    printf("Matched");
}

❌ Bad Practice:

if (x = 5) {   // Assignment instead of comparison!
    printf("Always true");
}

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📌 Summary – Recap & Next Steps

The if...else structure is essential for decision-making logic in C programs. It allows programs to respond to varying input, compare values, and execute code selectively.

🔍 Key Takeaways:

• Use if for simple conditions
• Add else if and else to handle multiple paths
• Use logical operators for compound conditions
• Avoid assignment = in place of comparison ==

⚙️ Real-World Relevance:

From form validation to game logic and system configuration, if...else is used in almost every C program that involves user input or dynamic response.

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❓ Frequently Asked Questions (FAQ)

❓ What is the difference between = and ==?

✅ = is an assignment operator.
✅ == checks for equality between two values.

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❓ Can I use multiple else if blocks?

✅ Yes. You can have as many else if blocks as needed to test multiple conditions.

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❓ What is nesting in if...else?

✅ Nesting means placing one if...else inside another. It helps test sub-conditions after a primary condition is true.

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❓ Can I use conditions without braces?

✅ Yes, but only for a single statement. For multiple statements, always use {} for clarity and to avoid bugs.

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❓ How do I compare strings using if?

✅ Use the strcmp() function from <string.h>:

if (strcmp(str1, str2) == 0) {
    // Strings are equal
}

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