Control Structures

Decision Making in C (if , if..else, Nested if, if-else-if )

Conditional statements (also known as decision control structures) in C, such as if, if-else, and switch, allow decision-making in programs by evaluating one or more conditions and directing the flow of program execution accordingly. They play a crucial role in determining which part of the code gets executed based on the evaluation of conditions.

Why Do We Need Conditional Statements?

In real-life scenarios, we often face situations where decisions need to be made based on certain conditions. Similarly, in programming, we use conditional statements to decide which block of code should be executed based on the evaluation of conditions. For example, in C, if condition x is true, execute block A; otherwise, execute block B. In cases where multiple conditions exist, we use structures like if-else-if or switch to handle them efficiently.

Types of Conditional Statements in C

1. if Statement
2. if-else Statement
3. Nested if Statement
4. if-else-if Ladder
5. switch Statement
6. Conditional (Ternary) Operator
7. Jump Statements (break, continue, goto, return)

1. if Statement in C : The if statement is the simplest form of decision-making. It executes a block of code only when a specified condition is true.

Syntax:

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

Example:

				
					#include <stdio.h>

int main() {
    int x = 10;

    if (x > 5) {
        printf("x is greater than 5\n");
    }

    printf("Program continues...\n");
    return 0;
}

Output:

				
					x is greater than 5
Program continues...

2. if-else Statement in C : The if-else statement provides a choice between two blocks of code: one that is executed if the condition is true and another that is executed if the condition is false.

Syntax:

				
					if (condition) {
    // Executes if condition is true
} else {
    // Executes if condition is false
}

Example:

				
					#include <stdio.h>

int main() {
    int x = 8;

    if (x > 10) {
        printf("x is greater than 10\n");
    } else {
        printf("x is less than or equal to 10\n");
    }

    return 0;
}

Output:

				
					x is less than or equal to 10

3. Nested if-else Statement in C : A nested if-else statement is an if statement inside another if statement. This allows for more complex decision-making.

Syntax:

				
					if (condition1) {
    if (condition2) {
        // Executes if both condition1 and condition2 are true
    } else {
        // Executes if condition1 is true and condition2 is false
    }
} else {
    // Executes if condition1 is false
}

Example:

				
					#include <stdio.h>

int main() {
    int x = 15;

    if (x > 10) {
        if (x < 20) {
            printf("x is between 10 and 20\n");
        } else {
            printf("x is 20 or more\n");
        }
    } else {
        printf("x is 10 or less\n");
    }

    return 0;
}

4. if-else-if Ladder in C : The if-else-if ladder is used to handle multiple conditions. It evaluates conditions from top to bottom, and the first condition that evaluates to true will have its associated block executed.

Syntax:

				
					if (condition1) {
    if (condition2) {
        // Executes if both condition1 and condition2 are true
    } else {
        // Executes if condition1 is true and condition2 is false
    }
} else {
    // Executes if condition1 is false
}

Example:

				
					#include <stdio.h>

int main() {
    int x = 15;

    if (x > 10) {
        if (x < 20) {
            printf("x is between 10 and 20\n");
        } else {
            printf("x is 20 or more\n");
        }
    } else {
        printf("x is 10 or less\n");
    }

    return 0;
}

5. switch Statement in C : The switch statement is an alternative to using multiple if-else conditions. It allows for a variable to be compared with different values, and the corresponding block of code is executed.

Syntax:

				
					switch (expression) {
    case value1:
        // Statements for value1
        break;
    case value2:
        // Statements for value2
        break;
    default:
        // Default statements
}

Example:

				
					Choice is 2

6. Conditional (Ternary) Operator in C : The conditional operator is a shorthand for the if-else statement. It uses three operands to evaluate a condition and return one of two values based on whether the condition is true or false.

Syntax:

				
					condition ? expression_if_true : expression_if_false;

Example:

				
					#include <stdio.h>

int main() {
    int x = 5;
    int result = (x > 0) ? 1 : 0;

    printf("Result: %d\n", result);

    return 0;
}

Output:

				
					Result: 1

7. Jump Statements in C : Jump statements are used for unconditional flow of control. They include:

break: Terminates a loop or switch statement.
continue: Skips the remaining code in the current iteration of a loop and starts the next iteration.
goto: Jumps to a labeled statement.
return: Exits the function and returns control to the caller.

Example of break:

				
					#include <stdio.h>

int main() {
    for (int i = 1; i <= 10; i++) {
        if (i == 6) {
            break;  // Terminates the loop when i is 6
        }
        printf("%d ", i);
    }
    return 0;
}

Output:

				
					1 2 3 4 5

if Statement

The if statement in C is a decision-making construct that allows you to execute a block of code based on a specified condition. It is one of the foundational concepts in C programming, enabling the inclusion of conditional logic to control the flow of the program.

Syntax:

				
					if (condition) {
    // Block of code to execute if the condition is true
}

Example:

Here is an example demonstrating the usage of the if statement:

				
					// C Program to demonstrate the usage of if statement
#include <stdio.h>

int main() {
    int num = 9;

    // if statement with a true condition
    if (num < 10) {
        printf("%d is less than 10\n", num);
    }

    // if statement with a false condition
    if (num > 20) {
        printf("%d is greater than 20\n", num);
    }

    return 0;
}

Output:

				
					9 is less than 10

Example:

In this example, we check whether a number is even or odd by using the modulus operator.

				
					// C Program to check if a number is even or odd
#include <stdio.h>

int main() {
    int num = 4956;

    // Check if the number is even
    if (num % 2 == 0) {
        printf("%d is Even\n", num);
    } 
    // Else, the number is odd
    else {
        printf("%d is Odd\n", num);
    }

    return 0;
}

Output:

				
					4956 is Even

if…else Statement

The if-else statement in C is a control flow mechanism used to make decisions in a program. It extends the basic if statement by adding an else block, allowing for the execution of an alternative set of statements when the if condition evaluates to false.

				
					if (condition) {
   // code executed when the condition is true
}

Example:

The following program demonstrates how the if-else statement works in C:

				
					// C Program to demonstrate the use of if-else statement
#include <stdio.h>

int main() {
    // if block with condition
    if (5 < 10) {
        // will be executed if the condition is true
        printf("5 is less than 10.");
    }
    // else block
    else {
        // will be executed if the condition is false
        printf("5 is greater than 10.");
    }

    return 0;
}

Output:

				
					5 is less than 10.

if-else-if Statement

The if-else-if ladder in C is a sequential structure used to test multiple conditions one after the other. If any condition evaluates to true, the corresponding block of code will execute, and the ladder will terminate. The conditions are tested only if all the preceding if or else-if conditions are false.

Syntax:

				
					if (condition) {
    // code to execute if condition is true
}
else if (condition) {
    // executed if the first condition is false 
    // and this condition is true
}
... // multiple else-if blocks can follow
else {
    // executed if all above conditions are false
}

Output:

				
					Using Prefix Increment on x = 8
Using Postfix Increment on y = 7

Working Flow of the if-else-if Ladder:

1. The program first enters the if block.
2. The first condition is evaluated:

If the condition is true, the corresponding code block is executed, and the ladder terminates.
If the condition is false, the program moves to the next else-if block.

3. The next else-if condition is evaluated:

If the condition is true, its associated block is executed, and the ladder terminates.
If the condition is false, the process continues with subsequent else-if blocks.

4. If none of the if or else-if conditions are true, the final else block is executed.

5. The program exits the if-else-if ladder after execution of the appropriate block.

Note: An else block is optional in an if-else-if ladder.
Example: Check Whether a Number is Positive, Negative, or Zero
In the following example, we check if a number is positive, negative, or zero using the if-else-if ladder:

				
					// C Program to check whether a number is positive, negative, or zero
#include <stdio.h>

int main() {
    int number = 0;

    // Condition for positive numbers
    if (number > 0) {
        printf("The number is Positive\n");
    }
    // Condition for negative numbers
    else if (number < 0) {
        printf("The number is Negative\n");
    }
    // Condition for zero
    else {
        printf("The number is Zero\n");
    }

    return 0;
}

Output:

				
					The number is Zero

Example of Decrement Operator:

				
					#include <stdio.h>

int main() {
    int a = 9;
    int b = 9;

    printf("Using Prefix Decrement on a = %d\n", --a);
    printf("Using Postfix Decrement on b = %d", b--);
    return 0;
}

Output:

				
					Using Prefix Decrement on a = 8
Using Postfix Decrement on b = 9

Switch Statement

The switch case statement in C is used to evaluate an expression and execute different blocks of code based on the matched case. It allows control to be transferred to various parts of a program depending on the evaluated value, making it an effective alternative to multiple if statements.

How Switch Case Works

The switch case statement follows a selection-control mechanism, where the value of a given expression determines which case block should execute. This can be particularly useful for simplifying long sequences of if-else statements that compare a variable to multiple possible values.

Syntax of Switch Statement in C

				
					switch (expression) {
    case value1:
        // code to execute when expression equals value1
        break;
    case value2:
        // code to execute when expression equals value2
        break;
    ...
    case value_n:
        // code to execute when expression equals value_n
        break;
    default:
        // code to execute if none of the cases match
}

How to Use Switch Case in C

Before using switch case, it’s important to understand the following rules:

The “case value” must be of char or int type.
You can have one or more cases.
Each case must have a unique value.
A break statement is optional but commonly used to prevent fall-through.
The default case is also optional but is used to handle values that don’t match any case.

Example:

				
					// C program to demonstrate the use of switch case statement
#include <stdio.h>

int main() {
    int day = 3;

    switch (day) {
        case 1:
            printf("Sunday");
            break;
        case 2:
            printf("Monday");
            break;
        case 3:
            printf("Tuesday");
            break;
        default:
            printf("Invalid day");
    }

    return 0;
}

How the Switch Statement Works

Step 1: The expression in the switch statement is evaluated.
Step 2: The value of the expression is compared with each case.
Step 3A: If a matching case is found, the associated block is executed.
Step 3B: If no matching case is found, the default case is executed (if present).
Step 4A: If the break keyword is present, the program exits the switch block.
Step 4B: Without break, execution falls through to the next case.
Step 5: The program continues executing the code after the switch statement.

Example: Switch Case Without Break

				
					// C program to demonstrate behavior without break
#include <stdio.h>

int main() {
    int var = 2;

    switch (var) {
        case 1:
            printf("Case 1 executed\n");
        case 2:
            printf("Case 2 executed\n");
        case 3:
            printf("Case 3 executed\n");
        default:
            printf("Default case executed\n");
    }

    return 0;
}

Output:

				
					Case 2 executed
Case 3 executed
Default case executed

Relational Operators in C

In C programming, loops are essential for performing repetitive tasks efficiently. The for loop allows a block of code to be executed repeatedly based on a given condition. It is a type of entry-controlled loop that is widely used for iterating through arrays, strings, and other data structures.

What is the `for` Loop in C?

The for loop in C is a control structure that repeats a block of statements a specified number of times. It is different from other loops like while and do-while because it contains initialization, condition checking, and updating statements all in one line.

Syntax of for Loop

				
					for (initialization; condition; update) {
    // code to be executed repeatedly
}

Structure of `for` Loop:

1. Initialization: Initializes the loop control variable. This step is executed only once, at the beginning of the loop.
2. Condition: This is the condition that is checked before each iteration of the loop. If the condition is true, the loop continues; otherwise, it terminates.
3. Body: The block of statements that is executed repeatedly as long as the condition is true.
4. Update: This is where the loop control variable is updated, usually by incrementing or decrementing, after every iteration.

How the `for` Loop Works

Step 1: Initialization is done at the start of the loop.
Step 2: The condition is evaluated. If it is true, the loop body is executed.
Step 3: After the body is executed, the loop control variable is updated.
Step 4: The loop repeats from Step 2, continuing until the condition becomes false.

Example of for Loop

				
					// C program to demonstrate for loop
#include <stdio.h>

int main() {
    int gfg;

    // for loop with initialization, condition, and update
    for (gfg = 1; gfg <= 5; gfg++) {
        printf("HelloWorld\n");
    }

    return 0;
}

Output:

				
					HelloWorld
HelloWorld
HelloWorld
HelloWorld
HelloWorld

while Loop

The while loop in C is an entry-controlled loop that executes a block of code repeatedly as long as the given condition remains true. It is one of the most common loops used in C programming.

Syntax of while Loop

				
					while (test expression) {
    // code block consisting of multiple statements
}

Example of while Loop

The following example demonstrates how to use a while loop in C:

				
					// C program to demonstrate while loop
#include <stdio.h>

int main() {
    // Initialization of loop variable
    int i = 0;

    // The loop will run while i is less than 5
    while (i < 5) {
        // Loop body
        printf("Hello, World\n");

        // Incrementing the loop variable
        i++;
    }
    return 0;
}

Output:

				
					Hello, World
Hello, World
Hello, World
Hello, World
Hello, World

Structure of `while` Loop

The while loop in C follows a structured approach, consisting of the following parts:

1. Initialization: Before the loop begins, a loop control variable is initialized. This step is essential for controlling the loop but is not part of the loop’s syntax.
2. Conditional Statement: This step checks whether the loop should continue. The loop body executes only if the condition is true. Once the condition becomes false, the loop terminates.
3. Body: The actual block of code that is executed as long as the condition is true. It is typically enclosed within curly braces {}.
4. Updation: After each iteration, the loop variable is updated (usually incremented or decremented).

How the while Loop Works

Step 1: The loop starts by evaluating the test condition.
Step 2A: If the condition is false, the loop terminates and control passes to the next part of the program.
Step 2B: If the condition is true, the loop body executes.
Step 3: After executing the loop body, control returns to Step 1 for the next iteration. This process continues until the condition becomes false.

do while Loop

In C programming, loops are control flow statements that allow a section of code to be executed repeatedly as long as a specified condition is true. Among the three types of loops in C—the do-while loop, while loop, and for loop—the do-while loop is particularly useful for iterating through arrays, vectors, and other data structures.

Syntax of do...while Loop in C

				
					do {
    // loop body (statements to execute)
} while (condition);

Example:

				
					// C Program to demonstrate do...while loop behavior
// when the condition is false from the start
#include <stdbool.h>
#include <stdio.h>

int main() {
    // Declaring a false condition
    bool condition = false;

    do {
        printf("This is the loop body.\n");
    } while (condition); // false condition

    return 0;
}

Output:

				
					This is the loop body.

Structure of `while` Loop

The do-while loop in C has a structured format with the following components:

1. Initialization: A loop control variable is initialized before the loop begins. This step is crucial for controlling the loop but is not part of the loop’s syntax.
2. Body: The main block of code to be executed is placed here. Unlike other loops, the body of the do-while loop runs at least once before the condition is checked. The code block is typically enclosed within curly braces {}.
3. Conditional Statement: After executing the loop body, the loop checks a condition. If the condition is true, the loop repeats from the start of the body. When the condition becomes false, the loop terminates.
4. Updation: Within the loop body, the control variable is usually updated (e.g., incremented or decremented) to progress toward the condition becoming false.

How the do while Loop Works

Step 1: The loop begins by executing the body of the loop at least once, regardless of the condition.
Step 2: After the loop body executes, the test condition is evaluated.
Step 2A: If the condition is false, the loop terminates, and control moves to the next part of the program.
Step 2B: If the condition is true, control returns to Step 1 to repeat the loop body.
Step 3: This process continues until the condition evaluates to false.

Contents

Control Structures

Decision Making in C (if , if..else, Nested if, if-else-if )

Why Do We Need Conditional Statements?

if Statement

if…else Statement

if-else-if Statement

Working Flow of the if-else-if Ladder:

Switch Statement

How Switch Case Works

Relational Operators in C

What is the `for` Loop in C?

Structure of `for` Loop:

How the `for` Loop Works

while Loop

Structure of `while` Loop

How the while Loop Works

do while Loop

Structure of `while` Loop

How the do while Loop Works

Related Chapters

CATEGORY

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Contents

Control Structures

Decision Making in C (if , if..else, Nested if, if-else-if )

Why Do We Need Conditional Statements?

if Statement

if…else Statement

if-else-if Statement

Working Flow of the if-else-if Ladder:

Switch Statement

How Switch Case Works

Relational Operators in C

What is the for Loop in C?

Structure of for Loop:

How the for Loop Works

while Loop

Structure of while Loop

How the while Loop Works

do while Loop

Structure of while Loop

How the do while Loop Works

Related Chapters

CATEGORY

ABOUT US

GET IN TOUCH

FOLLOW US

What is the `for` Loop in C?

Structure of `for` Loop:

How the `for` Loop Works

Structure of `while` Loop

Structure of `while` Loop