In C language, logical operators are used to combine multiple conditions or expressions, typically in conditional statements (if, while, etc.). These operators help control the flow of a program by evaluating multiple conditions together. There are three main logical operators in C: logical AND (&&), logical OR (||), and logical NOT (!). The result of a logical operation is either true (non-zero, usually 1) or false (0).

List of Logical Operators

1. Logical AND (&&):

   • Returns true if both operands are true. If either operand is false, the result is false.
   • Used when you want to check if all given conditions are true.
   • Example:

     int a = 5, b = 10;
     if (a > 0 && b > 0) {
         // This block will execute because both conditions are true.
     }
     

2. Logical OR (||):

   • Returns true if at least one operand is true. The result is false only if both operands are false.
   • Used when you want to check if any given condition is true.
   • Example:

     int a = 5, b = -3;
     if (a > 0 || b > 0) {
         // This block will execute because at least one condition (a > 0) is true.
     }
     

3. Logical NOT (!):

   • Reverses the truth value of the operand. If the operand is true, it returns false, and vice versa.
   • Used to invert a condition.
   • Example:

     int a = 5;
     if (!(a < 0)) {
         // This block will execute because a is not less than 0.
     }
     

Examples of Usage in Conditions

Logical operators are often used to create complex conditional statements:

#include <stdio.h>

int main() {
    int x = 5, y = 10, z = 15;

    // Logical AND
    if (x > 0 && y > 0 && z > 0) {
        printf("All numbers are positive.\n");
    }

    // Logical OR
    if (x > 10 || y > 10 || z > 10) {
        printf("At least one number is greater than 10.\n");
    }

    // Logical NOT
    if (!(x > 10)) {
        printf("x is not greater than 10.\n");
    }

    return 0;
}

Short-Circuit Evaluation

• AND (&&): If the first operand is false, the second operand is not evaluated because the whole expression will be false.
• OR (||): If the first operand is true, the second operand is not evaluated because the whole expression will be true.

For example:

int a = 0, b = 10;
if (a != 0 && b / a > 1) {
    // This will not evaluate "b / a" since "a != 0" is false, avoiding division by zero.
}

Important Points

1. Return Values: Logical operators return 1 (true) or 0 (false).
2. Combining Conditions: Logical operators are useful for combining multiple conditions in if, while, or for statements.

Summary

• Logical AND (&&): true if all conditions are true.
• Logical OR (||): true if at least one condition is true.
• Logical NOT (!): Inverts the truth value of a condition.

Logical operators are essential for controlling the flow of a program by allowing you to combine and manipulate conditions effectively, making decision-making more flexible and powerful.