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Table of contents
1.
Introduction
2.
Types of Logical Operators
2.1.
Logical AND (&&)
2.2.
C
2.3.
Logical OR (||)
2.4.
C
2.5.
Logical NOT (!)
2.6.
C
3.
Short Circuit Logical Operators
3.1.
Short Circuiting in Logical AND Operator
3.2.
C
3.3.
Short Circuiting in Logical OR Operator
3.4.
C
4.
Frequently Asked Questions
4.1.
What happens if I mix different logical operators in one statement?
4.2.
Can logical operators be used with non-boolean values?
4.3.
How do short-circuiting operators affect program performance?
5.
Conclusion
Last Updated: Mar 27, 2024
Medium

Logical Operators in C

Author Pallavi singh
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Introduction

When coding in C, logical operators are like the decision-makers in your code, helping it decide what path to take based on certain conditions. These operators are the building blocks that allow us to combine multiple conditions together & make more complex decisions in our programs. 

Logical Operators in C

In this article, we'll explore the different types of logical operators available in C, how they work, & how to use them effectively in your projects. 

Types of Logical Operators

In C programming, we use three main logical operators to test more than one condition. These operators help our programs make decisions based on multiple factors. Let's break them down one by one.

Logical AND (&&)

The logical AND operator, represented by &&, is like a strict rule that says both conditions must be true for the whole statement to be true. If you have two statements, let's say A & B, using A && B means both A & B need to be true for the result to be true. If either A or B is false, then the result will be false.

Here's a simple example to illustrate this:

  • C

C

#include <stdio.h>

int main() {

   int a = 5;

   int b = 10; 

 // Using the logical AND operator

   if (a > 0 && b > 0) {

       printf("Both numbers are positive.\n");

   } else {

       printf("At least one number is not positive.\n");

   }

   return 0;

}

Output

Both numbers are positive.

In this example, the program checks if both a & b are greater than 0. Since both conditions are true, it prints "Both numbers are positive."

Logical OR (||)

The logical OR operator, represented by ||, is more flexible. It says that if either of the conditions is true, then the whole statement is true. So, for two statements A & B, using A || B means if either A or B (or both) is true, the result will be true. If both A & B are false, then the result is false.

Let's see an example:

  • C

C

#include <stdio.h>

int main() {

   int a = -5;

   int b = 10;

   // Using the logical OR operator

   if (a > 0 || b > 0) {

       printf("At least one number is positive.\n");

   } else {

       printf("Both numbers are not positive.\n");

   }

  return 0;

}

Output

At least one number is positive.


In this case, even though a is not greater than 0, b is. So, the program prints "At least one number is positive."

Logical NOT (!)

The logical NOT operator, represented by !, flips the truth value of a condition. If a condition is true, using ! makes it false, & if it's false, ! makes it true. It's like saying "not this condition."

For example:

  • C

C

#include <stdio.h>

int main() {

   int a = 5;

   int b = 0;

  // Short circuiting with logical AND

   if (a < 10 && b == 0) {

       printf("Short circuit did not occur, both conditions checked.\n");

   }

   if (b == 0 && a < 10) {

       printf("Short circuit occurred, second condition not checked.\n");

   }

return 0;

}

Output

a is not greater than 10.


Here, a > 10 is false, but !(a > 10) turns it into true, so the program prints "a is not greater than 10."

These operators are the tools you'll use to make your programs "think" & make decisions based on different conditions. Understanding how to use them effectively is key to writing more complex & useful C programs.

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Short Circuit Logical Operators

In C programming, short circuiting is a smart way the program decides not to check further conditions if it already knows the outcome. This happens with logical AND && & logical OR || operators. Let's dive into how this works for each.

Short Circuiting in Logical AND Operator

Short circuiting might sound a bit technical, but it's actually a simple concept once you understand this. When using the logical AND (&&) operator in C, the computer takes a shortcut that can save time when running your code. This shortcut is called "short circuiting."

Here’s how it works with the logical AND operator: if the first condition is false, C doesn’t even bother to check the second condition because it already knows the whole statement can't be true. It's like if you have two switches in a row for a light to work, both need to be ON. If the first one is OFF, there's no point in checking the second one because the light won’t turn on anyway.

Let's see this in action with an example:

  • C

C

#include <stdio.h>

int main() {

   int a = 5;

   int b = 0;

  // Short circuiting with logical AND

   if (a < 10 && b == 0) {

       printf("Short circuit did not occur, both conditions checked.\n");

   }

   if (b == 0 && a < 10) {

       printf("Short circuit occurred, second condition not checked.\n");

   }

return 0;

}

Output

Output

In this code, both if statements are true, but the order of conditions matters for short circuiting. In the first if, C checks both conditions because the first one is true. In the second if, C doesn’t check the second condition (a < 10) because it already found b == 0 to be true, which is enough to satisfy the AND operation.

This might seem like a small detail, but it can make your code faster, especially if the second condition takes a lot of time to check. It's a smart way C helps optimize your programs without you having to do anything extra.

Short Circuiting in Logical OR Operator

Short circuiting doesn’t just happen with the logical AND operator; it also occurs with the logical OR (||) operator, but with a little twist. In this case, C looks for the first true condition. If it finds one, it skips checking the rest because just one true condition is enough to make the whole statement true.

Imagine you're told you can go out if it's a weekend or you've finished your homework. If it's already the weekend, you don't even need to mention your homework; you can go out either way.

Here's how it plays out in code:

  • C

C

#include <stdio.h>

int main() {

   int isWeekend = 1; // Let's say 1 is true

   int homeworkDone = 0; // 0 is false

  // Short circuiting with logical OR

   if (isWeekend || homeworkDone) {

       printf("You can go out!\n");

   } else {

       printf("You cannot go out.\n");

   }

  return 0;

}

Output

You can go out!


In this example, the program checks if it's the weekend (isWeekend is true). Since that's true, it doesn’t even look at homeworkDone. It already knows you can go out, so it prints "You can go out!"

This feature of logical OR short circuiting is super useful for avoiding unnecessary checks. If the first condition is enough to determine the result, why waste time on the second? It's another clever way C helps your programs run more efficiently.

Frequently Asked Questions

What happens if I mix different logical operators in one statement?

When you mix different logical operators like && and || in a single statement, C uses rules of precedence to decide which one to evaluate first. But, to avoid confusion & make your code clearer, it's best to use parentheses () to group conditions. This way, you control the order of evaluation & make your intentions clear to anyone reading your code.

Can logical operators be used with non-boolean values?

Yes, in C, you're not limited to using logical operators with just true or false values. Any non-zero number is treated as true, and zero is treated as false. This flexibility allows for more concise & versatile code, but be mindful of this behavior to avoid unexpected outcomes.

How do short-circuiting operators affect program performance?

Short-circuiting can improve your program's performance by reducing the number of operations it needs to perform. Especially in conditions that involve function calls or complex calculations, using short-circuiting wisely can make your code faster & more efficient.

Conclusion

Logical operators are a fundamental part of programming in C, allowing your code to make decisions based on multiple conditions. Understanding how to use &&, ||, and !, along with the concept of short-circuiting, will help you write more efficient and effective C programs. Remember, the key to mastering logical operators is practice, so try using them in different scenarios to see how they can best serve your programming needs.

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