Module 3: Operators in C

Learning Objectives

By the end of this module, you will be able to:

• Understand what operators are and how they work.
• Perform arithmetic calculations in C.
• Compare values using relational operators.
• Combine conditions with logical operators.
• Assign values using assignment operators.
• Use increment and decrement operators effectively.
• Perform bit-level operations using bitwise operators.
• Make decisions using the ternary operator.
• Understand operator precedence and associativity.
• Build simple programs using different operators.

Introduction

Operators are one of the most important building blocks of any programming language. They allow us to perform calculations, compare values, manipulate data, and make decisions.

For example:

• Add two numbers
• Check whether a student passed
• Find the largest of two numbers
• Test if a number is even or odd
• Perform binary operations for efficient programming

In C, operators work on operands (variables or values) to produce a result.

Example:

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1int sum = 10 + 5;

Here:

• 10 and 5 are operands.
• + is the operator.
• 15 is the result.

Types of Operators in C

C provides several categories of operators:

• Arithmetic Operators
• Relational Operators
• Logical Operators
• Assignment Operators
• Increment and Decrement Operators
• Bitwise Operators
• Ternary Operator
• Other Operators (covered in later modules)

Arithmetic Operators

Arithmetic operators perform mathematical calculations.

Addition

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1#include <stdio.h>
2
3int main()
4{
5    int a = 20;
6    int b = 10;
7
8    printf("%d", a + b);
9
10    return 0;
11}

Output

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130

Subtraction

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1printf("%d", 20 - 5);

Output

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115

Multiplication

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1printf("%d", 6 * 5);

Output

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130

Division

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1printf("%d", 20 / 5);

Output

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14

Integer Division

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1printf("%d", 5 / 2);

Output

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12

The decimal part is discarded because both operands are integers.

Floating-Point Division

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1printf("%.2f", 5.0 / 2);

Output

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12.50

Modulus Operator

Returns the remainder after division.

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1printf("%d", 10 % 3);

Output

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11

Common uses:

• Even/Odd checking
• Leap year calculation
• Circular indexing

Relational Operators

Relational operators compare two values.

The result is:

• 1 → True
• 0 → False

Example:

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1#include <stdio.h>
2
3int main()
4{
5    int a = 10;
6    int b = 20;
7
8    printf("%d\n", a < b);
9    printf("%d\n", a == b);
10
11    return 0;
12}

Output

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11
20

Logical Operators

Logical operators combine multiple conditions.

Logical AND (&&)

Returns true only if both conditions are true.

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1int age = 20;
2
3if(age >= 18 && age <= 60)
4{
5    printf("Eligible");
6}

Logical OR (||)

Returns true if at least one condition is true.

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1int marks = 85;
2
3if(marks >= 90 || marks >= 80)
4{
5    printf("Excellent");
6}

Logical NOT (!)

Reverses the result of a condition.

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1int isStudent = 0;
2
3if(!isStudent)
4{
5    printf("Not a student");
6}

Assignment Operators

Assignment operators assign values to variables.

Example:

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1int x = 10;
2
3x += 5;
4
5printf("%d", x);

Output

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115

Increment and Decrement Operators

These operators increase or decrease a variable by one.

Pre-Increment

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1int a = 5;
2
3printf("%d", ++a);

Output

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16

The value is increased before it is used.

Post-Increment

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1int a = 5;
2
3printf("%d", a++);
4printf("%d", a);

Output

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15
26

The current value is used first, then incremented.

Pre-Decrement

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1int a = 5;
2
3printf("%d", --a);

Output

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14

Post-Decrement

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1int a = 5;
2
3printf("%d", a--);
4printf("%d", a);

Output

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15
24

Bitwise Operators

Bitwise operators work directly on the binary representation of integers.

Bitwise AND

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1int a = 6;
2int b = 3;
3
4printf("%d", a & b);

Binary:

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16 = 110
23 = 011
3------------
4    010

Output

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12

Bitwise OR

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1printf("%d", 6 | 3);

Output

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17

Bitwise XOR

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1printf("%d", 6 ^ 3);

Output

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15

Bitwise NOT

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1printf("%d", ~5);

The exact result depends on the system's integer representation, but on most modern systems using two's complement, the output is:

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1-6

Left Shift

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1printf("%d", 5 << 1);

Output

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110

Equivalent to multiplying by 2 for positive integers.

Right Shift

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1printf("%d", 8 >> 1);

Output

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14

Equivalent to dividing by 2 for positive integers.

Ternary Operator

The ternary operator is a shorthand for if-else.

Syntax

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1condition ? expression1 : expression2;

Example:

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1#include <stdio.h>
2
3int main()
4{
5    int age = 20;
6
7    printf("%s", age >= 18 ? "Adult" : "Minor");
8
9    return 0;
10}

Output

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1Adult

Operator Precedence

Operator precedence determines the order in which operators are evaluated.

Example:

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1int result = 10 + 5 * 2;

Result:

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120

Multiplication is performed before addition.

Common Operator Precedence

Example

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1int value = (10 + 5) * 2;

Output

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130

Parentheses have the highest precedence.

Practice Project 1: Simple Calculator

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1#include <stdio.h>
2
3int main()
4{
5    float a, b;
6
7    printf("Enter two numbers: ");
8    scanf("%f %f", &a, &b);
9
10    printf("Addition = %.2f\n", a + b);
11    printf("Subtraction = %.2f\n", a - b);
12    printf("Multiplication = %.2f\n", a * b);
13
14    if (b != 0)
15        printf("Division = %.2f\n", a / b);
16    else
17        printf("Division by zero is not allowed.\n");
18
19    return 0;
20}

Practice Project 2: Even/Odd Checker

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1#include <stdio.h>
2
3int main()
4{
5    int number;
6
7    printf("Enter a number: ");
8    scanf("%d", &number);
9
10    if(number % 2 == 0)
11        printf("Even Number");
12    else
13        printf("Odd Number");
14
15    return 0;
16}

Practice Project 3: Largest Number

cCopy
1#include <stdio.h>
2
3int main()
4{
5    int a, b;
6
7    printf("Enter two numbers: ");
8    scanf("%d %d", &a, &b);
9
10    if(a > b)
11        printf("%d is the largest.", a);
12    else if(b > a)
13        printf("%d is the largest.", b);
14    else
15        printf("Both numbers are equal.");
16
17    return 0;
18}

Common Mistakes to Avoid

• Using = instead of == in comparisons.
• Dividing by zero without checking the denominator.
• Assuming integer division returns decimal values.
• Misunderstanding the difference between pre-increment (++a) and post-increment (a++).
• Ignoring operator precedence; use parentheses to make expressions clear.
• Using bitwise operators (&, |) when logical operators (&&, ||) are intended.

Best Practices

• Use parentheses to improve readability in complex expressions.
• Validate user input before performing operations like division.
• Prefer descriptive variable names such as totalMarks instead of x.
• Keep arithmetic expressions simple and readable.
• Use the ternary operator only for short, straightforward conditions.
• Learn operator precedence, but use parentheses whenever the evaluation order may be unclear.

Module Summary

In this module, you learned:

• What operators are and how they manipulate data.
• Arithmetic operators for mathematical calculations.
• Relational operators for comparing values.
• Logical operators for combining conditions.
• Assignment operators for updating variables efficiently.
• The difference between pre/post increment and decrement operators.
• How bitwise operators manipulate binary data.
• How to simplify conditional expressions using the ternary operator.
• The importance of operator precedence and associativity.
• How to apply these concepts by building a calculator, an even/odd checker, and a largest number finder.

After completing this module, you'll be ready to learn control statements (if, switch, loops, break, and continue), enabling your programs to make decisions and execute repetitive tasks efficiently.