C Programming Decision Making Statements If If Else Nested If Switch Case Complete Guide

C Programming Decision Making Statements: if, if-else, Nested if, and switch-case

if Statement

The if statement allows a single block of code to be executed if a specified condition is true. It's the simplest form of conditional statements.

Syntax:

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

• Condition: This is an expression that evaluates to either true (1) or false (0).
• Block of Code: The code placed within the curly braces {} will execute only if the condition evaluates to true.

Working Principle:

• The condition inside the parentheses () is evaluated.
• If the condition is true (non-zero), the code block within the curly braces {} is executed.
• If the condition is false (zero), the control moves to the next statement or block of code following the if statement.

Example:

int number = 5;
if (number > 3) {
    printf("The number is greater than 3\n");
}

if-else Statement

The if-else statement provides two paths for decision-making—when the condition is true, one block executes; when it's false, another block runs.

Syntax:

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

Working Principle:

• The condition is evaluated.
• If true, the first block of code executes.
• If false, the second block of code (following else) executes.

Example:

int age = 20;
if (age >= 18) {
    printf("You are eligible to vote.\n");
} else {
    printf("You are not eligible to vote.\n");
}

Nested if Statement

A nested if statement occurs when an if or if-else statement is placed inside another if or if-else statement. This structure allows for more complex conditions to be evaluated.

Syntax:

if (condition1) {
    if (condition2) {
        // Statements to be executed if both condition1 and condition2 are true
    } else {
        // Statements to be executed if condition1 is true but condition2 is false
    }
} else {
    // Statements to be executed if condition1 is false
}

Working Principle:

• The outer if statement's condition is evaluated first.
• If it's true, the inner if condition is evaluated.
  • If the inner if condition is true, the innermost block executes.
  • If the inner if condition is false, the else block associated with it executes.
• If the outer if condition is false, the else block after the outer if executes.

Example:

int grade = 90;
if (grade >= 60) {
    if (grade >= 90) {
        printf("Grade is A\n");
    } else {
        printf("Grade is B or C\n");
    }
} else {
    printf("Grade is below C\n");
}

Important Points:

• Nested if statements can lead to complex and difficult-to-maintain code. Use them judiciously.
• Indenting nested if statements improves readability.

switch-case Statement

The switch-case statement is used when there are multiple conditions depending on the value of the same variable. It's cleaner and more readable than using multiple if-else statements for such scenarios.

Syntax:

switch(expression) {
    case constant1:
        // Statements to be executed if expression == constant1
        break;
    case constant2:
        // Statements to be executed if expression == constant2
        break;
    ...
    default:
        // Statements to be executed if expression doesn't match any constant
        break;
}

Working Principle:

• The expression is evaluated once.
• The result of the expression is compared with the values of each case.
• If a match is found, the corresponding case's statements execute.
• If no match is found, the default case's statements execute.
• The break statement prevents the program from falling through to the next case.

Example:

char grade = 'B';
switch(grade) {
    case 'A':
        printf("Excellent!\n");
        break;
    case 'B':
    case 'C':
        printf("Well done\n");
        break;
    case 'D':
        printf("You passed\n");
        break;
    case 'F':
        printf("Better try again\n");
        break;
    default:
        printf("Invalid grade\n");
        break;
}

Important Points:

• The expression must evaluate to an integer type (int, char).
• You can use the same statement or series of statements for multiple cases.
• Use default to handle cases not covered by existing case labels.
• Each case must have a unique integral constant or character literal.
• The break statement is crucial to prevent fall-through.

Summary of Key Information

1. if Statement:

   • Executes code if the condition is true.
   • Single conditional path.

2. if-else Statement:

   • Executes different blocks of code based on a single condition.
   • Provides two possible execution paths.

3. Nested if Statement:

   • Allows multiple levels of conditions.
   • Can become complex; careful planning is necessary.
   • Indentation improves readability.

4. switch-case Statement:

   • Used for evaluating multiple possible values of a single expression.
   • Cleaner syntax for multiple conditions on the same variable.
   • Each case should have a unique constant value.
   • break prevents fall-through to subsequent cases.
   • default handles unexpected values.