Lectu 3: Operators in C

Page 2: Quick recap

• Last class…
  • C code organization
  • Compilation process
• Today's class…
  • Operators in C

Page 3: Arithmetic Operators and Precedence

• Arithmetic Operators and Precedence

  • Operator names, with their descriptions and examples:
  • + Addition: Adds together two values
    • Example: x + y
    • In code: sum = x + y;
    • Math representation: $x + y$
  • - Subtraction: Subtracts one value from another
    • Example: x - y
    • In code: sub = x - y;
    • Math representation: $x - y$
  • * Multiplication: Multiplies two values
    • Example: x * y
    • In code: mul = x * y;
    • Math representation: $x \cdot y$ or $x \times y$
  • / Division: Divides one value by another
    • Example: x / y
    • In code: div = x / y;
    • Math representation: $\frac{x}{y}$
  • % Modulus: Returns the division remainder
    • Example: x % y
    • In code: mod = x % y;
    • Math representation: not a simple single fraction, represents remainder $x \bmod y$

• Precedence note

  • Precedence of operators follows general math rules: multiplicative operators have higher precedence than additive operators; relational and logical operators typically have lower precedence than arithmetic operators.
  • For emphasis, multiplicative: $*,/,$ come before additive: $+, -$; then relational, then logical operators.

• General guidance

  • These rules affect evaluation order in expressions unless parentheses override order.

• Code example

  int main() {
    int x = 4, y = 3;
    int sum, sub, mul, div, mod;
    sum = x + y;
    sub = x - y;
    mul = x * y;
    div = x / y;
    mod = x % y;
  }

Page 5: Relational Operators

• Relational operators and their meanings
  • == Equal to
  • != Not equal
  • > Greater than
  • < Less than
  • >= Greater than or equal to
  • <= Less than or equal to
• Example code

  int main() {
    int x = 4, y = 3, res;
    res = x == y;
    res = x != y;
    res = x > y;
    res = x < y;
    res = x >= y;
    res = x <= y;
  }

• Notes
  • The expressions yield boolean-like results represented as integers in C (0 for false, nonzero for true).

Page 6: Logical Operators

• Logical operators and their semantics
  • && Logical and: Returns true if both statements are true
  • || Logical or: Returns true if one of the statements is true
  • ! Logical not: Reverses the result
• Example usage and conventions
  • In C, true is represented by a nonzero value; false is represented by 0. In many contexts, true is 1.
  • When using bool type, you typically include and use true/false literals.
• Example code

  #include <stdbool.h>
  int main() {
    bool x = true, y = false;
    bool res;
    res = x && y;  // false (0)
    res = x || y;  // true (1)
    res = !x || y; // false (0)
    res = 2 && 4;  // true (1) because both are nonzero
    res = 0 || !(-3); // 0 || true => true (1)
  }

• Important notes
  • False is 0; True is nonzero (commonly 1 when using bools).
  • The code sample shows that nonzero integers are treated as true in logical contexts.

Page 8: Bitwise Operators

• Bitwise operators and their purposes
  • & Bitwise AND: Returns 1 only if both bits are 1
  • | Bitwise OR: Returns 1 if at least one of the bits is 1
  • ^ Bitwise XOR: Returns 1 if the operands are different
• Descriptive caveat
  • Bitwise operators operate on individual bits and are distinct from logical operators; the latter operate on truthiness of entire expressions.
• Example code

  int main() {
    int a = 5; // Binary: 0101
    int b = 3; // Binary: 0011
    int result = a & b; // Result: 0001 (1 in decimal)
  }

Page 9: Assignment Operators

• Assignment operators and their equivalences
  • = C = A + B will assign the value of (A + B) to C
  • += C += A is equivalent to C = C + A
  • -= C -= A is equivalent to C = C - A
  • *= C *= A is equivalent to C = C * A
  • /= C /= A is equivalent to C = C / A
  • %= C %= A is equivalent to C = C % A
• Notes
  • These operators combine arithmetic with assignment in a single operation for brevity and clarity.

Page 10: Increment/Decrement Operators

• Increment and Decrement descriptions
  • ++ Increases the value of a variable by 1
  • -- Decreases the value of a variable by 1
• Prefix vs postfix
  • i++ Postfix increment: value used then incremented
  • ++i Prefix increment: value incremented then used
  • i-- Postfix decrement: value used then decremented
  • --i Prefix decrement: value decremented then used
• Example code

  int main() {
    int x = 4, res;
    res = x++;
    res = --x;
    x--;
    ++x;
  }

Page 11: Do Now — L3 Worksheet and Operators Quiz

• Activity setup
  • Do now: L3 Worksheet (join a partner, max. 3)
  • Q1.3 | Operators Quiz (individual)
• Context
  • NAU NORTHERN ARIZONA UNIVERSITY
• Purpose
  • Reinforce understanding of operators covered: arithmetic, relational, logical, bitwise, assignment, and increment/decrement.

Cross-page notes and context

• Quick recap of course framing
  • CS 136 - Computer Science II
  • Module 1: Introduction to C Programming
  • Topics include C code organization, compilation process, and operators in C
• Practical emphasis
  • Concrete examples demonstrate how to translate operator concepts into actual C code
  • Distinctions between similar concepts (logical vs bitwise, prefix vs postfix) highlighted across examples
• Foundational ties
  • These operators underpin control flow decisions, numerical computations, and data manipulation in C programs
• Real-world relevance
  • Understanding operator behavior is essential for correct program logic, optimization, and avoiding common pitfalls (e.g., operator precedence, boolean evaluation, and side effects in increments)
• Ethical/practical notes
  • Clear, correct code reduces bugs and maintenance burden, which aligns with professional software development ethics and quality standards