C Tutorial

Full List of Keywords in C Language (With Examples & Explanation)

Table of Contents

  • Introduction
  • What Are Keywords in C Language? Definition
  • Why Are Keywords Used in C Programming?
  • Full List of Keywords in C Language
  • All Keywords in C Explained
  • Most Important Keywords in C Programming Language
  • Keywords in C PDF
  • Keywords in C Language FAQs

Introduction

keywords in c

One of the fundamental building blocks of C is the keywords, which are reserved words that have a specific meaning and function in the language. 

In our previous write-ups, we talked about:

Now, in this write-up (part of a C programming tutorial for beginners), we will delve into the world of keywords in C language and explore their importance in writing efficient and effective code. 

We will look at the most commonly used keywords, as well as the syntax and usage of each. Whether you are a beginner or an experienced programmer, this guide will provide a comprehensive overview of the role that keywords play in the C language. 

What Are Keywords in C Language? Definition

Keywords in C programming language are reserved words that have a special meaning and are used to perform specific operations. You cannot use keywords as identifiers, such as variable names, function names, or any other user-defined names. 

Keywords in C language are part of the syntax and structure of the language,

Every word that developers use in C is either a keyword or an identifier. Keywords have a fixed meaning, and the meaning is not editable or changeable. 

Keywords are essential parts of the C programming language, and they are always written in lowercase (small case) letters of the alphabet. 

Every language has some words that are used internally, and a user can not change the meaning of it. These are known as keywords or sometimes reserved keywords. These are used to avoid confusion between compilers and programmers.

Why Are Keywords Used in C Programming?

If you are a beginner, you might wonder why we use keywords in C language. Here is the answer.

Using keywords helps the compiler understand what the programmer intends to do in the code. For example, the keyword "int" is used to declare an integer variable, and the keyword "for" is used to create a loop.

By using keywords in C programming language, the programmer can easily communicate the structure and intent of the code, making it easier to understand and maintain. Additionally, keywords help prevent naming conflicts and make the code more readable, as their meaning is well-defined in the language.

Full List of Keywords in C Language

There are 32 keywords in C programming language. 

Here is the C keywords list:

  1. auto

  2. break

  3. case

  4. char

  5. const

  6. continue

  7. default

  8. do

  9. double

  10. else

  11. enum

  12. extern

  13. float

  14. for

  15. goto

  16. if

  17. int

  18. long

  19. register

  20. return

  21. short

  22. signed

  23. sizeof

  24. static

  25. struct

  26. switch

  27. typedef

  28. union

  29. unsigned

  30. void

  31. volatile

  32. while

All 32 keywords in C were added in the first version of C, which was known as the C89 standard. There were some keywords added in the C with the C99 standard, which are:

  • _bool

  • _complex

  • _imaginary

  • restrict

  • inline

Every keyword in C is used for a purpose as it is designed for a unique purpose. It can not be used as variable names as per user concern. It has a special meaning in compilers. Using it without proper spelling or using it in the upper case alphabet will show compile time error.

The main is not a keyword, but it should be used like one as it holds special value in the compilers. If main is used as a keyword in the program as using it as a variable might confuse the compiler, which will result in an error.

All Keywords in C Explained

Here is a detailed explanation of the purpose of each keyword in C:

1. auto

The auto keyword is used to declare a local variable. It is optional and is the default storage class for local variables.

2. break

The break keyword is used to break out of a loop or switch statement. It is used to terminate the execution of a loop or switch statement before the conditions specified in the loop or switch statement have been met.

3. case

The case keyword is used in switch statements to define a case for the switch expression to match against.

4. char

The char keyword is used to declare a variable of type char, which is a data type that can store a single character.

5. const

The const keyword is used to declare a constant value that cannot be changed during the execution of the program.

6. continue

The continue keyword is used to skip the current iteration of a loop and continue with the next iteration.

7. default

The default keyword is used in switch statements to define the default case that will be executed if none of the other cases match the switch expression.

8. do

The do keyword is used to start a do-while loop, which is a type of loop that executes the loop body at least once and then continues to loop as long as the specified condition is true.

9. double 

The double keyword is used to declare a variable of type double, which is a data type that can store a double-precision floating-point value.

10. else

The else keyword is used in conjunction with the if keyword to define an else block that will be executed if the condition specified in the if statement is not true.

11. enum

It is used to declare an enumerated type, which is a user-defined data type that consists of a set of named values.

12. extern

It is used to declare a variable or function that is defined in another file.

13. float

The float keyword is used to declare a variable of type float, which is a data type that can store a single-precision floating-point value.

14. for

The for a keyword is used to start a for loop, which is a type of loop that allows you to repeat a set of statements a specified number of times.

15. goto 

The goto keyword is used to transfer control to a label within a function. The use of the goto statement is generally discouraged, as it can make code harder to read and understand.

16. if

The if keyword is used to start an if statement, which is used to conditionally execute a block of code based on the value of a specified condition.

17. int

The int keyword is used to declare a variable of type int, which is a data type that can store a whole number.

18. long

The long keyword is used to declare a variable of type long, which is a data type that can store a larger whole number than the int data type.

19. register 

The register keyword is used to declare a variable that should be stored in a register instead of in memory. This can improve the performance of the program by reducing the time required to access the variable.

20. return 

It is used to return a value from a function back to the calling function.

21. short 

The short keyword is used to declare a variable of type short, which is a data type that can store a smaller whole number than the int data type.

22. signed

It is used to declare a variable of type signed int, which is a data type that can store a whole number with a positive or negative value.

23. sizeof

It is used to determine the size, in bytes, of a variable, data type, or expression.

24. static

It is used to declare a static variable, which is a variable that retains its value between function calls.

25. struct

It is used to declare a structure, which is a user-defined data type that can contain multiple values of different data types.

26. switch 

The switch keyword is used to start a switch statement, which is used to conditionally execute a block of code based on the value of a specified expression.

27. typedef 

The typedef keyword is used to create an alias for a data type, making it easier to declare variables of that type in the future.

28. union

The union keyword is used to declare a union, which is a user-defined data type that can contain multiple values of different data types, but only one value can be stored in the union at a given time.

29. unsigned 

The unsigned keyword is used to declare a variable of type unsigned int, which is a data type that can store only positive whole numbers.

30. void 

The void keyword is used to declare a function that does not return a value or to declare a pointer to an unknown data type.

31. volatile

It is used to declare a variable that can be modified by an external process or by a hardware interrupt. This keyword is used to prevent the compiler from optimizing access to the variable, as the value of the variable may change unexpectedly.

32. while

The "while" keyword in C is used to create a loop that continues to execute a block of code as long as a specified condition is true.

Most Important Keywords in C Programming Language

Some of the most important keywords are:

  • int: used to declare integer variables

  • char: used to declare character variables

  • float: used to declare floating-point variables

  • double: used to declare double-precision floating-point variables

  • return: used to return a value from a function

  • void: used to declare a function that does not return a value

  • if: used to perform conditional statements

  • else: used to execute code if the condition in the "if" statement is not met

  • while: used to create a loop that continues while a condition is true

  • for: used to create a loop with a counter

  • break: used to exit a loop prematurely

  • continue: used to skip the current iteration of a loop and move on to the next one

  • do: used to create a do-while loop, which executes at least once before checking the condition

  • switch: used to perform multiple branches based on the value of a variable

  • case: used within a switch statement to specify a branch

  • default: used within a switch statement to specify a default branch if none of the other cases is met.

These are just some of the most commonly used keywords in C, but there are many more. It's important to have a good understanding of these keywords and their uses, as they form the backbone of the C language and are used extensively in many programs.

Keywords in C PDF

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Keywords in C Language FAQs

Below are some of the most frequently asked questions about the list of keywords in C programming:

1. What is the volatile keyword in C?

The volatile keyword in C is a type qualifier that is used to indicate to the compiler that the value of a variable can change unexpectedly. When a variable is declared as volatile, the compiler assumes that its value can be changed by hardware or software outside of the control of the program, and it will not perform any optimizations that would assume otherwise.

The volatile keyword is commonly used in embedded systems programming or in programs that interact with hardware devices. In these cases, the value of a variable may be changed by an external process, such as an interrupt service routine, without the program's knowledge. 

By declaring a variable as volatile, the compiler will always read its value from memory rather than using a cached value, ensuring that the most up-to-date value is used in the program.

Here's an example of how to declare a volatile variable:

volatile int value;

In this example, the variable value is declared as a volatile int. This means that the value of value can change unexpectedly, and the compiler will not make any assumptions about its value.

2. What is an extern keyword in C?

The extern keyword in C is used to declare a variable or function that is defined in another source file. When a variable or function is declared with the extern keyword, it indicates to the compiler that the actual definition of the variable or function can be found in another source file and that the declaration is simply an external reference to it.

The extern keyword is often used in larger projects to manage the scope of variables and functions across multiple source files. 

For example, if you have a variable or function that you need to use in multiple source files, you can declare it with the extern keyword in each source file that needs to access it, and then define it in a single source file.

Here's an example of how to declare an extern variable:

// file1.c
extern int my_variable;
// file2.c
#include
int my_variable = 10;
int main()
{
    printf("%d\n", my_variable);
    return 0;
}

In this example, the variable my_variable is declared with the extern keyword in file1.c. The definition of my_variable is then provided in file2.c. When the program is compiled and linked, the definition of my_variable from file2.c will be linked to the declaration in file1.c, and both source files will be able to access the same variable.

3. What is the register keyword in C?

The register keyword in C is a type qualifier that is used to suggest to the compiler that a variable should be stored in a register instead of in memory. When a variable is declared as a register, it indicates to the compiler that the variable will be heavily used and that it is a good candidate to be stored in a register.

Registers are a small amount of fast storage that is built into the processor. By storing a frequently used variable in a register, the program can access it more quickly, as the processor can access the value stored in a register much faster than it can access a value stored in memory.

It's important to note that the compiler is free to ignore the register keyword and store the variable in memory if it determines that it is not beneficial to store it in a register. The use of the register keyword is simply a suggestion to the compiler.

Here's an example of how to declare a register variable:

register int value;

In this example, the variable value is declared as a register int. This means that the compiler is being asked to store the variable in a register if possible, as it is expected to be heavily used in the program.

4. How many keywords are there in C?

There are 32 keywords in the C programming language.

5. What are the most commonly used keywords in C?

Some of the most commonly used keywords in C include "int", "char", "float", "while", "for", "if", "else", "return", "void", and "switch".

6. What does the keyword "int" do in C?

The keyword "int" is used to declare an integer variable in C.

7. What does the keyword "while" do in C?

The keyword "while" is used to create a loop that continues to execute a block of code as long as a specified condition is true.

8. What is the difference between "for" and "while" loops in C?

The "for" loop is used when the number of iterations is known beforehand, while the "while" loop is used when the number of iterations is not known beforehand. The "for" loop also has a counter that is incremented with each iteration, while the "while" loop simply continues to execute as long as the condition is true.

9. What is the use of the keyword "if" in C?

The keyword "if" is used to perform conditional statements in C. It allows the program to execute different code blocks based on whether a specified condition is true or false.

10. What does the keyword "void" do in C?

The keyword "void" is used to declare a function in C that does not return a value.

11. What is the use of the keyword "switch" in C?

The keyword "switch" is used to perform multiple branches in C based on the value of a specified variable. It is often used as an alternative to a series of "if-else" statements.

12. Can keywords in C be used as variable names?

No, keywords in C cannot be used as variable names or identifiers. They have a specific meaning and function in the language and cannot be redefined.

13. What is the importance of keywords in C?

Keywords are important in C because they help the compiler understand what the programmer intends to do in the code. By using keywords, the programmer can easily communicate the structure and intent of the code, making it easier to understand and maintain.

14. Can new keywords be added to C?

No, new keywords cannot be added to C. The set of keywords in C is fixed and standardized.

15. How do I use keywords in C?

Keywords in C are used as part of the syntax and structure of the language. They have a specific meaning and function, and their usage varies depending on the keyword. It is important to have a good understanding of the keywords and their uses in order to write efficient and effective code in C.

This was all about the main C language keywords. In the next chapters, we will talk about:

And more. Visit the main page of our comprehensive C Language Tutorial for Beginners to check the complete list of topics we have covered, including an introduction to C Programming, its features, history, etc.

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