What Are Control Statements?

A simple C program without control statements runs line by line from top to bottom. Control statements change this normal flow. They allow the program to:

• Decide whether to execute a block of code or skip it.
• Choose between two or more blocks of code.
• Repeat some statements (loops – we will see in the next lessons).

In this article we focus on the selection or decision-making control statements: they select which block of code should run based on a condition.

Conditions and Boolean Results in C

All control statements in this lesson use a condition inside parentheses: if (condition). A condition is usually a relational or logical expression, for example:

• marks >= 50
• temp < 20
• a == b
• age >= 18 && age <= 60

In C, each condition is evaluated to an integer value: 0 means false, and any non-zero value means true.

int marks = 65;

if (marks >= 50) {      // condition is true (1)
    printf("PASS\\n");
}

The Simple if Statement

The simplest decision-making statement in C is if. It executes a block of code only when a condition is true.

Syntax

if (condition) {
    // statements to execute when condition is true
}

If the condition is false, the statements inside the braces are skipped. The program continues after the closing brace.

Example – Turn on Fan if Temperature Is High

#include <stdio.h>

int main() {
    float temp;
    printf("Enter temperature: ");
    scanf("%f", &temp);

    if (temp > 30.0f) {
        printf("Fan ON (temperature is high)\\n");
    }

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

If the user enters 35, the condition temp > 30.0f is true, so the program prints both lines. If the user enters 25, the condition is false and only “Program finished.” is printed.

The if-else Statement

Very often we want to do one thing when a condition is true, and a different thing when it is false. For that we use if-else.

Syntax

if (condition) {
    // statements when condition is true
} else {
    // statements when condition is false
}

Example – Pass or Fail

#include <stdio.h>

int main() {
    int marks;
    printf("Enter your marks: ");
    scanf("%d", &marks);

    if (marks >= 50) {
        printf("Result: PASS\\n");
    } else {
        printf("Result: FAIL\\n");
    }

    return 0;
}

Here the program will always print exactly one of the two messages. There is no third option.

Example – Even or Odd

int num;
printf("Enter an integer: ");
scanf("%d", &num);

if (num % 2 == 0) {
    printf("Number is EVEN\\n");
} else {
    printf("Number is ODD\\n");
}

Nested if Statements

A nested if means having one if (or if-else) statement inside another. This is useful when decisions depend on previous decisions.

Example – Check Eligibility for Loan

Imagine we want to approve a small loan only if:

• Age is between 21 and 60, and
• Salary is greater than or equal to 20,000.

#include <stdio.h>

int main() {
    int age;
    float salary;

    printf("Enter age: ");
    scanf("%d", &age);

    if (age >= 21 && age <= 60) {
        printf("Enter monthly salary: ");
        scanf("%f", &salary);

        if (salary >= 20000.0f) {
            printf("Loan can be APPROVED\\n");
        } else {
            printf("Loan REJECTED: salary too low\\n");
        }
    } else {
        printf("Loan REJECTED: age not in allowed range\\n");
    }

    return 0;
}

Note that we first check age. Only if age condition is satisfied, we ask for salary and check it. This structure keeps input interactions logical and efficient.

The else-if Ladder

Sometimes we need to choose between more than two options. For example, grading marks into A, B, C, D, or “Fail”. Using separate if statements would be confusing, so we use an else-if ladder.

Syntax

if (condition1) {
    // block 1
} else if (condition2) {
    // block 2
} else if (condition3) {
    // block 3
} else {
    // default block
}

The conditions are checked from top to bottom. As soon as one condition is true, its block is executed and the rest are skipped.

Example – Grading System

#include <stdio.h>

int main() {
    int marks;
    printf("Enter marks (0-100): ");
    scanf("%d", &marks);

    if (marks >= 90) {
        printf("Grade: A+\\n");
    } else if (marks >= 80) {
        printf("Grade: A\\n");
    } else if (marks >= 70) {
        printf("Grade: B\\n");
    } else if (marks >= 60) {
        printf("Grade: C\\n");
    } else if (marks >= 50) {
        printf("Grade: D\\n");
    } else {
        printf("Grade: F (Fail)\\n");
    }

    return 0;
}

Notice that we only use the lower bound in each condition. For example, if marks are 85, the first condition (marks >= 90) is false, the second (marks >= 80) is true, so the remaining conditions are not checked.

Example – Electricity Tariff Slabs

A more practical example is a simple tariff calculator.

float units, rate;

printf("Enter units consumed: ");
scanf("%f", &units);

if (units <= 100) {
    rate = 1.5f;
} else if (units <= 300) {
    rate = 2.0f;
} else if (units <= 500) {
    rate = 3.0f;
} else {
    rate = 4.0f;
}

printf("Rate per unit = %.2f\\n", rate);

Best Practices for if/else Code

// Hard to read
if (age >= 18 && age <= 60 && salary >= 15000 && experience >= 2) { ... }

// Easier to read
int isAdult = (age >= 18 && age <= 60);
int hasMinimumSalary = (salary >= 15000);
int hasExperience = (experience >= 2);

if (isAdult && hasMinimumSalary && hasExperience) { ... }

#define PASS_MARK 50

if (marks >= PASS_MARK) { ... }

Common Mistakes with if, if-else and else-if Ladder

1. Using = Instead of ==

if (x = 5) {   // WRONG: this assigns 5 to x, then checks if x is non-zero
    ...
}

Use == when you want to compare.

if (x == 5) {   // CORRECT: check if x is equal to 5
    ...
}

2. Unwanted Semicolon After if

if (marks >= 50);   // WRONG: semicolon ends the if
{
    printf("PASS\\n"); // this will always execute
}

Remove the extra semicolon.

3. Missing Braces Around Multiple Statements

if (marks >= 50)
    printf("PASS\\n");
    printf("Congratulations!\\n");  // always prints

// Use braces:
if (marks >= 50) {
    printf("PASS\\n");
    printf("Congratulations!\\n");
}

4. Confusing Nested if with else-if

Sometimes new programmers write nested if when an else-if ladder is simpler and more efficient. For example:

// Less clear
if (marks >= 90) {
    ...
} else {
    if (marks >= 80) {
        ...
    } else {
        if (marks >= 70) {
            ...
        }
    }
}

Better:

if (marks >= 90) { ... }
else if (marks >= 80) { ... }
else if (marks >= 70) { ... }
else { ... }

Small Practice Programs Using if / if-else / else-if

1. Maximum of Two Numbers

   if (a > b) {
       printf("Max = %d\\n", a);
   } else {
       printf("Max = %d\\n", b);
   }

2. Maximum of Three Numbers (nested if)

   int max;
   
   if (a > b) {
       if (a > c) {
           max = a;
       } else {
           max = c;
       }
   } else {
       if (b > c) {
           max = b;
       } else {
           max = c;
       }
   }

3. Simple Menu Using else-if Ladder

   int choice;
   printf("1. Add\\n2. Subtract\\n3. Multiply\\nEnter choice: ");
   scanf("%d", &choice);
   
   if (choice == 1) {
       printf("You selected Addition\\n");
   } else if (choice == 2) {
       printf("You selected Subtraction\\n");
   } else if (choice == 3) {
       printf("You selected Multiplication\\n");
   } else {
       printf("Invalid choice\\n");
   }

Quick Checklist Before You Compile

• Is every if condition enclosed in parentheses ( )?
• Did you use == for comparison instead of =?
• Are braces { } correctly placed and balanced?
• Is there any unwanted semicolon directly after if?
• Have you chosen between nested if and else-if ladder in a clean way?

Suggested Featured Image Concept

You can use the following description as a prompt in your image generation tool:

“Flat 16:9 illustration on a light background. A flowchart-style diagram shows a C program starting at the top, then splitting at a diamond decision box labeled `if (condition)` into ‘Yes’ and ‘No’ paths, leading to blocks named `if`, `if-else`, `nested if`, and `else-if ladder`. A laptop on the side displays short C code examples with `if`, `else if`, and `else` highlighted in blue. At the bottom-right, a young South Indian / Tamil technician character stands with a pointer explaining the flow. Title text at the top: ‘Control Statements in C’ and subtitle: ‘if, if-else, nested if, else-if ladder | Tamil Technicians’. Clean vector style, minimal colors, educational look.”