Logical Operators in C Languages

Erukulla's November 15, 2016

Understanding Logical Operators in C Programming

Logical operators play a crucial role in decision-making within C programming. They allow programmers to combine and test multiple conditions, leading to informed decisions. In C, there are three main logical operators: Logical AND (&&), Logical OR (||), and Logical NOT (!).

Overview of Logical Operators

Logical expressions in C combine two or more relational expressions, yielding a value of either 1 (true) or 0 (false). The zero value signifies false, while any non-zero value signifies true. It's important to note that Logical AND and Logical OR are binary operators, while Logical NOT is a unary operator.

Operator Precedence

The Logical NOT (!) operator takes the highest precedence over Logical AND (&&) and Logical OR (||). When operators with equal precedence exist, they are evaluated from left to right, except for Logical NOT, which follows right-to-left associativity.

Logical AND (&&)

The result of a Logical AND expression is true only when both relational expressions are true. The syntax for Logical AND is exp1 && exp2. Let's look at some examples:

  1. If a = 10, b = 5, c = 15, and i = (a > b) && (b < c), the value of i will be 1.
  2. If a = 10, b = 5, c = 15, and i = (a < b) && (b < c), the value of i will be 0.

Truth table for Logical AND:

exp1 exp2 exp1 && exp2
T T T
T F F
F T F
F F F

Logical OR (||)

The result of a Logical OR expression is false only when both relational expressions are false. The syntax for Logical OR is exp1 || exp2. Here are examples:

  1. If a = 10, b = 5, c = 15, and i = (a < b) || (b < c), the value of i will be 1.
  2. If a = 10, b = 5, c = 15, and i = (a < b) && (b > c), the value of i will be 0.

Truth table for Logical OR:

exp1 exp2 exp1 || exp2
F F F
F T T
T F T
T T T

Logical NOT (!)

The result of a Logical NOT expression is true if the expression is false and vice versa. The syntax for Logical NOT is !exp1. Examples include:

  1. If a = 10, b = 5, c = 15, and i = !((a < b) && (b < c)), the value of i will be 1.
  2. If x = 20 and i = !(x == 20), the value of i will be 0 because x == 20 is true, and !i = 0.

Truth table for Logical NOT:

Exp !Exp
T F
F T

De Morgan's Rule:

  1. !(x && y) is equivalent to !x || !y
  2. ii. !(x || y) is equivalent to !x && !y

These rules provide a convenient way to express negations of compound expressions.

Operator Precedence Summary

  • Highest: !
  • Next: > >= < <=
  • Next: == !=
  • Next: &&
  • Lowest: ||

Example: The value of !(3 && 4 >= 7 || 6) is 1

Understanding logical operators is fundamental for writing efficient and effective C programs. These operators allow programmers to create intricate decision-making structures, leading to well-optimized and reliable code.

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