Decision Making in C

Until now, every C program you have written executes statements one after another in a fixed order. However, real-world applications need to make decisions based on different conditions.

For example,

• Should a student pass or fail?
• Is a person eligible to vote?
• Which of two numbers is greater?
• Should a discount be applied?

Decision-making statements allow programs to choose different paths based on conditions.

In C, this is achieved using if, if-else, else-if ladder, nested if, and switch statements.

🎯 Learning Objectives

After completing this lesson, you will be able to:

• Understand decision-making.
• Write programs using if.
• Use if-else.
• Create multiple conditions using else-if.
• Write nested if statements.
• Use the switch statement.
• Understand when to use each statement.

📖 What is Decision Making?

Decision making allows a program to execute different blocks of code depending on whether a condition is true or false.

Example

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Condition

↓

True  → Execute Block A

False → Execute Block B

Conditions in C

Conditions are expressions that evaluate to:

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1 → True

0 → False

Example

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age >= 18

marks > 40

salary < 50000

a == b

The if Statement

The if statement executes a block of code only if the condition is true.

Syntax

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if(condition)
{
    statements;
}

Example 1

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#include <stdio.h>

int main()
{
    int age = 20;

    if(age >= 18)
    {
        printf("Eligible to Vote");
    }

    return 0;
}

Output

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Eligible to Vote

Example 2

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#include <stdio.h>

int main()
{
    int marks = 90;

    if(marks >= 35)
    {
        printf("Pass");
    }

    return 0;
}

Output

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Pass

The if-else Statement

Sometimes we need another block if the condition is false.

Syntax

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if(condition)
{
    statements;
}
else
{
    statements;
}

Example

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#include <stdio.h>

int main()
{
    int marks = 28;

    if(marks >= 35)
    {
        printf("Pass");
    }
    else
    {
        printf("Fail");
    }

    return 0;
}

Output

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Fail

Real-Life Example

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#include <stdio.h>

int main()
{
    int age;

    printf("Enter Age: ");

    scanf("%d",&age);

    if(age >= 18)
        printf("Eligible for KauraX Student Ambassador");

    else
        printf("Not Eligible");

    return 0;
}

else-if Ladder

When there are multiple conditions, we use the else-if ladder.

Syntax

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if(condition1)
{

}
else if(condition2)
{

}
else if(condition3)
{

}
else
{

}

Grade Calculator

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#include <stdio.h>

int main()
{
    int marks;

    printf("Enter Marks: ");

    scanf("%d",&marks);

    if(marks >= 90)
        printf("Grade A");

    else if(marks >= 75)
        printf("Grade B");

    else if(marks >= 60)
        printf("Grade C");

    else if(marks >= 35)
        printf("Grade D");

    else
        printf("Fail");

    return 0;
}

Nested if

An if statement inside another if statement is called a nested if.

Syntax

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if(condition1)
{
    if(condition2)
    {

    }
}

Example

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#include <stdio.h>

int main()
{
    int age = 22;
    int idCard = 1;

    if(age >= 18)
    {
        if(idCard == 1)
        {
            printf("Entry Allowed");
        }
    }

    return 0;
}

switch Statement

The switch statement is used when a variable can have multiple fixed values.

Syntax

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switch(expression)
{
    case value1:

        statements;

        break;

    case value2:

        statements;

        break;

    default:

        statements;
}

Example

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#include <stdio.h>

int main()
{
    int day = 3;

    switch(day)
    {
        case 1:
            printf("Monday");
            break;

        case 2:
            printf("Tuesday");
            break;

        case 3:
            printf("Wednesday");
            break;

        case 4:
            printf("Thursday");
            break;

        default:
            printf("Invalid Day");
    }

    return 0;
}

Output

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Wednesday

Why break is Important?

Without break, execution continues to the next case.

Wrong

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case 1:
printf("Monday");

case 2:
printf("Tuesday");

Output

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Monday
Tuesday

Correct

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case 1:
printf("Monday");
break;

if vs switch

Practical Example

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#include <stdio.h>

int main()
{
    int choice;

    printf("===== KauraX Menu =====\n");

    printf("1. Courses\n");
    printf("2. Compiler\n");
    printf("3. Mock Test\n");
    printf("4. Exit\n");

    printf("Enter Choice: ");

    scanf("%d",&choice);

    switch(choice)
    {
        case 1:
            printf("Opening Courses...");
            break;

        case 2:
            printf("Opening Compiler...");
            break;

        case 3:
            printf("Opening Mock Tests...");
            break;

        case 4:
            printf("Thank You!");
            break;

        default:
            printf("Invalid Choice");
    }

    return 0;
}

Common Beginner Mistakes

Using = instead of ==

Wrong

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if(age = 18)

Correct

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if(age == 18)

Forgetting Curly Braces

Wrong

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if(age>=18)

printf("Eligible");

printf("Done");

Only the first statement belongs to the if.

Forgetting break

Wrong

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case 1:

printf("One");

Execution continues.

Missing Default Case

Always include

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default:

to handle unexpected values.

Using = instead of == inside an if condition is one of the most common programming mistakes made by beginners.

Best Practices

• Keep conditions simple.
• Indent code properly.
• Use braces even for single statements.
• Prefer switch for menu-driven programs.
• Use meaningful variable names.

🧠 Interview Questions

1. What is decision making?
2. Difference between if and if-else.
3. Explain the else-if ladder.
4. What is a nested if?
5. What is the purpose of the switch statement?
6. Why is break used?
7. Difference between if and switch.

✍ Practice Questions

1. Check whether a number is positive or negative.
2. Find the largest of two numbers.
3. Find the largest of three numbers.
4. Check whether a student passed or failed.
5. Create a calculator using switch.
6. Print the day of the week using switch.
7. Check whether a person is eligible to vote.

📚 Lesson Summary

In this lesson, you learned:

• Decision Making
• if Statement
• if-else Statement
• else-if Ladder
• Nested if
• switch Statement
• break Statement
• Common Mistakes
• Best Practices

Decision-making statements make programs intelligent by allowing them to choose different actions based on conditions.

🚀 What's Next?

In the next lesson, Loops in C, you'll learn:

• while Loop
• do-while Loop
• for Loop
• Nested Loops
• Infinite Loops
• Pattern Programs
• Practical Examples
• Interview Questions

Loops allow programs to repeat tasks efficiently without writing the same code multiple times.

Happy Coding with KauraX 💙