Operators and Expressions: Types, Precedence, and Associativity

Introduction to Operators and Expressions

An operator is a symbol that tells the compiler to perform specific mathematical, relational, or logical manipulations. The data items upon which operators act are called operands. An expression is a sequence of operators and operands that specifies a computation.

Classification of Operators

C supports a rich set of operators, which can be categorized as follows:

1. Arithmetic Operators

These are used for numerical calculations.

• + (Addition), - (Subtraction), * (Multiplication), / (Division), % (Modulus).
• Note: The % operator can only be used with integers.

2. Relational Operators

Used to compare two values. They return 1 (true) or 0 (false).

• == (Equal to), != (Not equal to), > (Greater than), < (Less than), >= (Greater than or equal to), <= (Less than or equal to).

3. Logical Operators

Used to combine multiple conditions.

• && (Logical AND), || (Logical OR), ! (Logical NOT).

4. Assignment Operators

Used to assign values to variables.

• Simple: =
• Compound: +=, -=, *=, /=, %=. (e.g., a += 5 is equivalent to a = a + 5).

5. Increment and Decrement Operators

These are unary operators used to increase or decrease a value by 1.

• Prefix (++a, --a): The value is changed first, then used in the expression.
• Postfix (a++, a--): The current value is used in the expression first, then changed.

Example:

int a = 5, b;
b = ++a; // a becomes 6, b becomes 6
b = a++; // b becomes 6, a becomes 7

6. Bitwise Operators

These perform operations at the bit level.

• & (AND), | (OR), ^ (XOR), ~ (NOT), << (Left shift), >> (Right shift).

7. Conditional (Ternary) Operator

The ?: operator is a shorthand for if-else statements.

• Syntax: condition ? expression1 : expression2;
• If the condition is true, expression1 is executed; otherwise, expression2 is executed.

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Operator Precedence and Associativity

When an expression contains multiple operators, the compiler follows a specific hierarchy:

Precedence: Decides which operator is evaluated first. Associativity: Decides the direction of evaluation when operators have the same precedence.

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Worked Example: Expression Evaluation

Evaluate: x = 5 + 3 * 2 / 4 % 2;

1. Multiplication (*) and Division (/) have higher precedence than +.
2. 3 * 2 = 6
3. 6 / 4 = 1 (Integer division)
4. 1 % 2 = 1
5. 5 + 1 = 6
6. x = 6

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Comparison Table: Operators

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Exam Tip

• Always show the difference between Prefix and Postfix: Examiners frequently ask for a code snippet demonstrating the difference.
• Precedence Tables: You do not need to memorize the entire table, but you must know the order: Unary > Arithmetic > Relational > Logical > Assignment.
• Bitwise Questions: If asked about bitwise operators, always include a small binary conversion example (e.g., 5 & 3 where 0101 & 0011 = 0001).
• Conditional Operator: When asked about the conditional operator, provide a clear syntax and a simple example like finding the maximum of two numbers.