Control Statements

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Last Updated on: 23rd Jan 2025 11:15:57 AM

If-Else

The if-else statement in C is a core control flow mechanism that lets your program make decisions. It executes different sets of code depending on whether a condition is true or false. Let's break it down simply and in detail:

1. The if Statement (Basic Form)

The simplest form checks a single condition:

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

• if (condition): The condition is an expression that evaluates to either true (any non-zero value) or false (zero). It's enclosed in parentheses ().
• { ... } (Code Block): The code inside the curly braces {} is the body of the if statement. This code runs only if the condition is true.

Example:

#include <stdio.h>

int main() {
    int temperature = 25;

    if (temperature > 20) {
        printf("It's a warm day!\n");
    }

    return 0;
}

Here, temperature > 20 is true (25 is greater than 20), so "It's a warm day!" is printed. If temperature was 15, nothing would be printed.

2. The else Statement (Adding an Alternative):

The else keyword provides a block of code to execute when the if condition is false:

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

Example:

#include <stdio.h>

int main() {
    int temperature = 10;

    if (temperature > 20) {
        printf("It's a warm day!\n");
    } else {
        printf("It's a cold day!\n");
    }

    return 0;
}

Now, because temperature is 10 (not greater than 20), the else block executes, printing "It's a cold day!"

3. The else if Statement (Checking Multiple Conditions):

else if lets you check multiple conditions sequentially:

if (condition1) {
    // Code if condition1 is true
} else if (condition2) {
    // Code if condition1 is false AND condition2 is true
} else if (condition3) {
    // Code if condition1 and condition2 are false AND condition3 is true
} else {
    // Code if ALL conditions are false
}

Example (Grading System):

#include <stdio.h>

int main() {
    int score = 85;

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

    return 0;
}

Here, the conditions are checked in order. score >= 80 is the first true condition, so "Grade: B" is printed, and the rest are skipped.

4. Nested if Statements (Conditions within Conditions):

You can put if statements inside other if or else blocks:

if (outer_condition) {
    if (inner_condition) {
        // Code if BOTH outer_condition AND inner_condition are true
    } else {
        // Code if outer_condition is true BUT inner_condition is false
    }
}

5. Key Points and Best Practices

• Curly Braces {}: Even if a block has only one statement, always use curly braces. This makes your code clearer and prevents errors if you add more statements later.
• Comparison Operators: Conditions use operators like:
  • == (equal to)
  • != (not equal to)
  • > (greater than)
  • < (less than)
  • >= (greater than or equal to)
  • <= (less than or equal to)
• Logical Operators: Combine conditions with:
  • && (AND): Both conditions must be true.
  • || (OR): At least one condition must be true.
  • ! (NOT): Inverts a condition's truth value.
• Indentation: Indent the code inside if, else if, and else blocks. This greatly improves readability.

#include <stdio.h>

int main() {
    int age = 25;
    char hasLicense = 'Y'; // 'Y' for yes, 'N' for no

    if (age >= 18 && hasLicense == 'Y') {
        printf("You are eligible to drive.\n");
    } else {
        printf("You are not eligible to drive.\n");
    }

    return 0;
}

This checks if the person is at least 18 and has a license.

The if-else statement is fundamental for creating programs that can handle different situations and make decisions based on data. Understanding it well is crucial for C programming..

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