C Operator – Logic Operators in C Programming

In this article, you will learn about the three logical operators in C.

I will first explain what operators are in programming and list the different types of operators available in C.

Then, you will learn the role logical operators have and how to use them with the help of code examples along the way.

Let's get into it!

What Is An Operator in Computer Programming?

In computer programing, an operator is a character, symbol, keyword, or combination of those. It determines what action gets performed on one or more operands.

An operand is an individual data item that gets manipulated by the operator.

Each high-level programming language defines these built-in characters and uses them to tell the compiler to perform arithmetic, relational or logical operations that manipulate data items and then return a final result.

What Are The Different Types of Operators in C Programming?

In C programming, operators fall into one of three categories:

• Unary operators
• Binary operators
• Ternary operators

Unary operators operate on a single operand. Some of the unary operators in C are:

• Arithmetic operators such as the increment operator(++), which increments the value of the operand by 1. And the decrement operator(--), which decrements the value of the operand by 1.
• Logical operators like the NOT(!) operator. This operator reverses the logical value of the operand – it changes true to false and false to true.
• Bitwise operators like the NOT(~) operator, which changes each 0 bit to 1 and each 1 bit to 0.

Binary operators operate on two operands. Some of the binary operators in C are:

• Arithmetic operators (+, -, *, /, %). These operators perform mathematical calculations on numerical data such as addition, subtraction, multiplication, division, and finding the remainder.
• Equality/Relational operators (==, !=, >, <, >=, <=). These operators compare two values and determine if one operand is greater than, less than, equal to, or not equal to the other operand.
• Logical/Conditional operators such as the AND(&&) and OR(||) operators.
• Bitwise operators ((&, |, ^, <<, >>), which treat data items as a sequence of bits (that is, 0s and 1s).
• Assignment operators (=, +=, -=, *=, /=, %=), which assign a specific value to a variable.

The Ternary operator (?:) operates on three operands. The general syntax looks something similar to the following:

(condition) ? expression1 : expression2;

The ternary operator is a conditional operator you can use as a shorthand for an if..else statement. It performs comparisons and returns a result.

What Is the Role of Logical Operators in C Programming?

You will see logical operators commonly used in conditional statements (such as if..else statements) since they aid in decision making – they determine what action should take place and what code should run next based on conditions you set.

You combine logical operators with one or multiple conditions to create a logical expression.

The logical operators evaluate the logical expression and return a result.

The result is always a Boolean value. A Boolean value determines whether the expression is true or false.

There are three logical operators in C programming: logical AND(&&), logical OR(||), and logical NOT (!).

Let's go into more detail on each one in the following sections.

How to Use the AND (&&) Logical Operator in C Programming

The logical AND(&&) operator checks whether all operands are true – the result is true only when all operands are true.

Here is the truth table for the AND(&&) operator when you are working with two operands:

Something to note here is that, when the first operand is false, the second operand is not evaluated.

Let's look at an example:
The result of (10 == 10) && (20 == 20) is true because both operands are true – (10 == 10) is true and (20 == 20) is true.

Let's look at another example:
The result of (10 == 20) && (20 == 20) is false because one of the operands is false – in this case, the first operand is false, so the second operand doesn't get evaluated.

Now, let's see how you can use the && operator in an if statement:

#include <stdio.h>

int main(void) {
  int a = 20;
  int b = 30;

  if (a > 10 && b > 10)
    printf("Both numbers are greater than 10\n");
}

// output

// Both numbers are greater than 10

In the example above, the output is Both numbers are greater than 10 because the condition a > 10 && b > 10 is satisfied.

Both a > 10 and b > 10 are true, so the result is true.

If either a or b did not satisfy the condition, then there would be no output in the console since I have not specified an else condition.

How to Use the OR (||) Logical Operator in C Programming

The logical OR(||) operator checks whether one of the operands is true – the result is true if at least one of the operands is true.

Here is the truth table for the OR(||) operator when you are working with two operands:

Note that with the OR (||) operator, if the first operand is true, then the second operator is not evaluated.

Let's look at an example:
The result of (10 == 20) || (20 == 20) is true because at least one of the operands is true, in this case, it is the second operand, even if the first operand is false.

Let's look at another example:
The result of (20 == 20) || (10 == 20) is true because one of the operands is true – in this case, since the first operand is true, the second one is not evaluated.

Now, let's see how you can use the OR (||) operator in an if statement:

#include <stdio.h>

int main(void) {
  int a = 20;
  int b = 5;

  if (a > 10 || b > 10)
    printf("At least one of the numbers is greater than 10");
}

In the example above, the output is At least one of the numbers is greater than 10 because the condition a > 10 || b > 10 is satisfied – at least one of the operands is true.

The first condition, a > 10, is true, so the result is true.

If both a and b were false, there would be no output.

How to Use the NOT (!) Logical Operator in C Programming

The logical NOT(!) operator negates the operand – that is, it returns the opposite of the operand.

If the operand is true, it returns false.

And if it is false, it returns true.

Here is the truth table for the NOT(!) operator:

Let's look at an example:
The result of !(10 == 10) is false.

The condition 10 == 10 is true, but the ! operator negates it.

And let's look at another example:
The result of !(10 == 20) is true.

The condition 10 == 20 is false, but the ! operator negates it.

Now, check the example below for how you can use the NOT(!) operator in an if statement:

#include <stdio.h>

int main(void) {
  int a = 20;
  int b = 5;

  if ( a > b)
    printf("a is greater than b\n");
}

The output is a is greater than b because the condition a > b is true.

However, if you used the NOT(!) operator, the condition is no longer true, so there would be no output:

#include <stdio.h>

int main(void) {
  int a = 20;
  int b = 5;

  if ( !(a > b))
    printf("a is greater than b\n");
}

Conclusion

And there you have it! You now know how the three logical operators work in C programming.

To learn more about C, give this C beginner's handbook a read to become familiar with the basics of the language.

Thanks for reading, and happy coding!