Operators & Expressions: Arithmetic, Relational, Logical, Bitwise, Assignment & Special

TAKEAWAYS

• Operators are symbols that perform operations on variables/values (e.g., +, ==, &&).
• Precedence and associativity dictate evaluation order (e.g., * before +).
• Relational (>, <=) and logical (&&, ||) operators enable decision-making.
• Bitwise operators (<<, &) manipulate binary data (used in compression, encryption).
• Assignment (=, +=) and comma operators chain operations.
• Type casting ensures correct data conversion (e.g., (int)3.7).

1. Introduction to Operators

Operators are symbols that perform operations on operands (variables/values). They are categorized into arithmetic, relational, logical, bitwise, assignment, and special operators.

1.1 Types of Operators

2. Arithmetic Operators

Perform mathematical operations.

2.1 Operators and Examples

flowchart TD
    A["Arithmetic Operators"] --> B["+" Addition]
    A --> C["-" Subtraction]
    A --> D["*"] Multiplication
    A --> E["/"] Division
    A --> F["%" Modulus]
    A --> G["++" Increment]
    A --> H["--" Decrement]

Example:

int a = 10, b = 3;
printf("%d\n", a / b);    // Output: 3 (integer division)
printf("%d\n", a % b);    // Output: 1 (remainder)

2.2 Precedence and Associativity

• Precedence (highest to lowest): %, *, /, +, -.
• Associativity: Left-to-right for same precedence.

Example:

int x = 10 + 2 * 3;  // 2*3 first → 16

3. Relational Operators

Compare two values and return 1 (true) or 0 (false).

3.1 Operators and Truth Tables

Example:

int a = 7, b = 5;
printf("%d\n", a > b);  // Output: 1 (true)

4. Logical Operators

Combine relational expressions.

4.1 Operators and Truth Tables

Example:

int x = 4, y = 5;
printf("%d\n", (x > 2) && (y < 10));  // Output: 1 (true)

5. Bitwise Operators

Manipulate binary data (used in low-level programming).

5.1 Operators and Examples

flowchart TD
    A["Bitwise Operators"] --> B["&"] Bitwise AND
    A --> C["|"] Bitwise OR
    A --> D["^"] Bitwise XOR
    A --> E["~"] Bitwise NOT
    A --> F["<<"] Left Shift
    A --> G[">>"] Right Shift
    A --> H["~="] Bitwise NOT Equal
    A --> I["&="] Bitwise AND Assignment
    A --> J["|="] Bitwise OR Assignment
    A --> K["^="] Bitwise XOR Assignment

Example (Bitwise AND):

int a = 5 (0101), b = 3 (0011);
printf("%d\n", a & b);  // Output: 1 (0001)

Real-World Use:

• eSewa’s Transaction Checks: Bitwise operations verify checksums in digital payments.
• Compression Algorithms: XOR (^) is used in data encryption (e.g., AES).

6. Assignment Operators

Assign values with shorthand.

Example:

int x = 5;
x += 3;  // x becomes 8

7. Special Operators

7.1 Comma Operator (,**)

Evaluates expressions left-to-right and returns the last value.

Example:

int a = (x = 2, y = 3, x + y);
printf("%d\n", a);  // Output: 5 (last evaluated)

7.2 Ternary Operator (?:)

Conditional expression: condition ? expr1 : expr2.

Example:

int max = (a > b) ? a : b;

7.3 sizeof Operator

Returns size (in bytes) of a variable/type.

Example:

printf("%d\n", sizeof(int));  // Output: 4 (on most systems)

8. Operator Precedence Table

9. Type Casting

Convert one data type to another.

Example:

float f = 3.14;
int i = (int)f;  // i becomes 3 (truncated)

Real-World Use:

• Daraz Discounts: Converting float prices to int cents for calculations.
• Bank Loans: Converting interest rates (double) to int for monthly payments.

10. Worked Example: eSewa Transaction Validation

Scenario: Verify if a transaction amount is within eSewa’s limits (₹10–₹10,000).

#include <stdio.h>
int main() {
    float amount = 500.50f;
    int valid = (amount >= 10) && (amount <= 10000);
    printf("Transaction %s\n", valid ? "valid" : "invalid");
    return 0;
}

Output:

Transaction valid

11. In the Real World

1. eSewa/Khalti

   • Logical Operators (&&) check if both payment details and amount are valid before processing.
   • Bitwise Operators (^) encrypt transaction IDs for security.

2. Daraz Order Processing

   • Relational Operators (>, <) prioritize orders based on urgency (e.g., if (order_time < 10) { rush_delivery = true; }).

3. NTC/Ncell Signal Strength

   • Bitwise Shifts (<<) adjust signal thresholds in mobile networks (e.g., threshold = 3 << 2 sets a 12-unit limit).

12. Exam Tip

• Always check precedence when combining operators (e.g., a = b + c * d evaluates c*d first).
• Logical operators (&&, ||) return 1/0, not true/false (unlike Java).
• Bitwise tricks are rarely needed for basic exams but appear in low-level coding questions.
• Practice type casting—exams often test implicit vs. explicit conversions.
• Memorize precedence table—it’s the #1 question in past exams.

Key Formula: For expressions like a = b + c * d, always parenthesize to avoid errors:

a = (b + c) * d;  // Different from b + (c * d)