C programming Keywords: A list and Explanation of Usage

C programming Keywords: A list and Explanation of Usage

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Updated on Jun 1, 2023 14:54 IST

Keywords in C refer to a set of reserved words with predefined meanings that are used to write programs in the C programming language. These keywords cannot be used as identifiers or variable names, as they have a specific function within the language. There are many C programming Keywords.In this aticle all keywords are explained with programming examples.

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Keywords play an essential role in any programming language as they define the structure or implementation of any program. The important part is to know about keywords that will aid the expertise of several imperatives in programming to the learner. In this article, we will let you see the list of keywords in c programming with their usage and explanation. 

int volatile void unsigned union typedef switch struct
for sizeof signed short auto while long register
if goto static float extern enum else double
do default const continue char case break return

  All these words are the 32 reserved keywords of c language. Its usage makes the programming language readily and more convenient to understand.

Keywords are predefined. These reserved words have special meanings to the compiler. Let’s dive deep into the keywords with their explanation and usage. 

Table of contents

Reserved keywords

1. while 

While is a loop that iterates a specific block of code until a particular condition turns true. 

To get the picture of the while loop, let’s move on to its flowchart.

2023_02_image-127.jpg

C program to demonstrate the use of while keyword

 
#include<stdio.h>
int main(){
int x=1; //initializing the value of x
//loop will execute until the value of x turns greater than 15
while(x<=15){
printf("%d ",x);
x++; //in each iteration ++operator increment the value of x by 1.
}
return 0;
}
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Output

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15        

Explanation 

In the above example, the value of x is initialized as 1, and the control of the program jumps to the expression of while; if it is true, then it runs the code written in while till the condition fails. 

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2. static 

A keyword that can be used with variables and functions in c programming is the static keyword. While ordinary variable has their scope limited to a definite extent, the scope of static variable is limited throughout the program.

Syntax of static keyword for variable 

Static datatype variable_name;

Syntax of static keywords for functions

Static type_of_function function_name()

3. if 

In c programming,” if” is a decision-making statement that is used when a condition is evaluated as true only. 

If the condition mentioned in the if block evaluates as true, then the code written in the if block gets executed. 

Example –

 
#include <stdio.h>
int main()
{
int u = 500;
int v = 1000;
if (u<v)
{
printf(" v is greater than u");
}
return 0;
}
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Output

 v is greater than u

4. else

else keyword is used with if in the decision-making statement of c programming. If the condition evaluates as true code of the if block will execute and in the case of false, the else part will execute. 

Example 

 
#include <stdio.h>
int main()
{
int u,v;
printf("enter two values");
scanf("%d%d",&u,&v);
if (u<v)
{
printf(" %d is greater than %d",v,u);
}
else
{
printf("%d is less than %d",v,u);
}
}
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Output

enter two values20

4

4 is less than 20

Also read: If-else Statement in C

5. volatile

volatile keyword in c programming is a qualifier just like the const keyword. It creates a volatile object that the hardware of the machine can modify. When a variable is described as volatile, it reports to the compiler that its value can be changed at any time without any involvement of the compiler. 

The volatile keyword can be used with pointers, register, etc. 

Syntax to declare a variable as volatile. 

volatile int variable_name;

Int volatile variable_name;

6. sizeof

sizeof is a unary operator in c programming that is used to calculate the size of any operand or data type. 

Program to demonstrate the use of sizeof operator 

 
#include <stdio.h>
int main()
{
printf("with the help of sizeof operator, size of some data types are given below.");
printf("%lu\n", sizeof(float));
printf("%lu\n", sizeof(char));
printf("%lu\n", sizeof(double));
printf("%lu", sizeof(int));
return 0;
}
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Output

with the help of the sizeof operator, the size of some data types is given below.4

1

8

4

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7. goto

goto is a jump statement in c programming that is used to shift the control of the program from one part to another part of the program.

Syntax 

goto label;

Label: statement ;

Program to demonstrate the use of goto statement in c

 
#include <stdio.h>
int main()
{
int n,x=1; //declaring variable
printf("enter any number:");
scanf("%d",&n); //taking input from user
printf("table of %d is given below:\n",n);
table_:
printf("%d x %d = %d\n",n,x,n*x);
x++; //increment value of x by 1
if(x<=5)
goto table_; //shifting the control of the program to label.
}
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Output-

enter any number:9

table of 99 is given below:

99 x 1 = 99

99 x 2 = 198

99 x 3 = 297

99 x 4 = 396

99 x 5 = 495

8. void

 In c programming, void stands for nothing, if a function return no value then it can be declared as a void function. A void function doesn’t accept any parameter and has no value or type. 

9. for

In c programming, for is used to iterate a part or code of the program several times as per the condition given in the loop. 

Syntax:

for (initialization statement; expression; update statement) {

 // code

}

Program to demonstrate the use of for loop

 
Program to demonstrate the use of for loop
#include <stdio.h>
int main() {
int n, i, sum = 0;
printf("how many times do you want to print statement ");
scanf("%d", &n);
//for loop terminates when n is less than i
for(i = 1; i <= n; ++i) {
printf("it is for loop.\n");
}
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Output

how many times do you want to print statement 4

it is for loop.

it is for loop.

it is for loop.

it is for loop.

10. int

int is a keyword that is used to declare the type of a variable. Here int stands for an integer, meaning it can have both positive and negative numbers but no decimal number.

If you use an integer value in your program, the variable must be declared an integer.

Size:4 bytes

Range:-32768 to 32767

Syntax

int variable_name;

int a; -32768 to 32767

Here, a is a variable of integer type.

Int a,b;

One can declare multiple variables as well at a time.

Example 

Program to demonstrate the use of int 

 
#include<stdio.h>
int main(){
int x;
{
x=2;
printf(" x holds an integer value that is:%d ",x);
}
return 0;
}
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Output-

 x holds an integer value that is:2 

11. signed

 the signed keyword is a type modifier used for a variable that can also take negative, zero, and positive integers.

signed char

Size: 1

Range:-128 to 127

12. unsigned

the unsigned keyword is a type modifier that is used for a variable that can take only positive integers and zero.

unsigned int

Size: 4

Range: 0 to 65535

unsigned char

Size: 1 byte

Range:0 to 255

Syntax 

unsigned char variable_name= value;

13. short

Considering c programming, short is a keyword that is used to declare a variable that holds the value of a signed integer.

Size: 2 bytes

Range: -32768 to 32767

unsigned short 

Size: 2 bytes

Range: 0 to 65535

14. long

the long keyword is a type modifier that is used for a variable that can take integers with bigger values.

Size: 4 bytes

Range: -2147483648 to 214743648 

15. extern

In c programming, an extern keyword is used to declare a global variable. Here extern stands for external, a variable declared as extern is a global variable that can be accessed anywhere in the c programming. 

Syntax of enum in c programming

extern data_type variable_name;

16. char

char stands for the character, which is a data type. Char allowed a variable to store a single character in it. 

Size: 1 byte

Range: -128 to 127 

 
#include"stdio.h"
void main() {
char ex_;
ex_ = 'a' ;
printf("%c \n",ex_);
}
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Output  

     a

17. float

Float is a data type used to declare a variable with a decimal value. It represents the floating-point number in c with 6 decimal digits in precision.

Size: 4 bytes 

Range:3.4E +/- 38 (7 digits)

example-

 
#include<stdio.h>
#include<string.h>
int main() {
float var_a = 11.11;
printf("The float value : %f",var_a);
return 0;
}
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Output

The float value: 11.110000

18. double

double is a data type that is used to declare a variable that holds 15 decimal digits in precision. Additionally, it represents the floating-point number in c.

Size – 8 bytes

Range 1.7E-308 to 1.7E+308

Syntax

 double name_of_variable;

Example

 
#include<stdio.h>
#include<string.h>
int main() {
double var_a = 114.1156;
printf("The double value : %f",var_a);
return 0;
}
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Output 

The double value: 114.115600

19. const

In c programming, any variable that is declared as const its value will not be changed in the execution of the program. In simple words, the value of a variable is constant in the whole program, and it can’t be changed. 

Program to demonstrate the use of the const keyword in c 

 
#include<stdio.h>
int main(){
const int my_number=626;
printf("my favourite number is: %d",my_number);
return 0;
}
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Output

my favourite number is: 626

20. typedef

typedef is a keyword in c programming that can be used with arrays, structures, and pointers. Typedef is used to redefine the existing data type’s name for user convenience.

Syntax 

typedef data_type New_name;

21. register

If a variable is stored in a register instead of a CPU, then it is easy to access. With the use of the register keyword, one can store the frequently used variable in the register for faster accessibility. 

Syntax

register data_type variable_name;

22. enum

 In c programming, an enum is a data type defined by the user that is used to allow names to the constant integrals or integers. Enum is the short term for the word enumeration. 

Syntax to declare an enum 

enum name_of_enum{constant1,constant2,constant3,constantn};

23. switch 

One can run a specific code using a switch case statement among different available choices. The switch statement takes an expression(must be an integer or character), and if it evaluates as true, then the case corresponding to that value gets executed.

Flowchart 

2023_02_image-115.jpg

Program to choose any subject using switch case

 
#include <stdio.h>
int main() {
char a; //declaring character variable
printf("Choose any category between (A, B): ");
scanf("%c", &a);
switch(a)
{
case 'A':
printf("You have selected biotechnology");
break;
case 'B':
printf("You have selected computer science");
break;
// value of a doesn't match any case constant that is A, B
default:
printf("oops! invalid choice");
}
return 0;
}
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Output-

Choose any category between (A, B): B

You have selected computer science

Output-

Choose any category among (A, B): C

oops! invalid choice

24. case

The case is a keyword in c that is used with the switch statement. 

The switch statement takes arguments, and if it evaluates as true, the case corresponding to that value gets executed.

 Refer to the above example of the switch keyword to understand the case in c programming.

25. default

default keyword is used in the switch case, which is the decision control statement of c programming. Considering the switch statement, when an expression entered by the user doesn’t match any case, the code under the default statement gets executed.

In the example of the switch case, the default statement executes when the user enters C, which is an invalid choice.

26. break

break keyword is used to stop the execution of code block in switch case and terms of the loop like for, do, while it terminates the loop by ending the execution of specific code block.

Example

 
#include<stdio.h>
#include<stdio.h>
void main ()
{
int x;
for(x = 0; x<15; x++)
{
printf("%d ",x);
if(x == 11)
break;
}
printf("\n when the value of x turns 11, the loop ends here!!");
}
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Output

0 1 2 3 4 5 6 7 8 9 10 11

 when the value of x turns 11, the loop ends here!!

27. continue

The continue keyword is used as the loop control statement; if the condition mentioned in the loop is evaluated as true, then the continue keyword compels the program’s control to run the next iteration of the loop. With the use of the continue keyword, lines of the code can be skipped.  

28. union

union is a data type available in c programming that aids in storing different data types at the same location in memory. It is similar to structure, while it has different memory locations for different data types. 

Syntax of union 

 
union name_of_union{
datatype variable1;
datatype variable;
};
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29. do

Concerning c programming, do is a keyword that is used with the while as a control flow statement. Do- while loop is used when the user wants to execute a loop at least once. 

Syntax

 
do{
statements;
}while(condition);
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30. struct 

struct stands for structure, in which we can group the variable of different data types like int, float, char, double, etc.

In terms of an array is a collection of similar types of data elements, while a structure is a collection of different types of data elements. In structure, different variables of the different data types are called the structure’s members.

Using the struct keyword, one can create the structure.

Syntax 

 
struct structure_name{ //structure declaration
int variable_name; //members of structure
char variable_name;
double variable_name;
};
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Program to demonstrate the use of the struct keyword 

 
#include<stdio.h>
struct structExample {
int a;
char c;
};
int main() {
// Create a structure variable of myStructure called s
//to access the members of structExample using the "." operator
struct structExample s;
s.a = 100;
s.c = 'z';
//Assigning values to the member of structure structExample
// Print values
printf("my favourite number %d\n", s.a);
printf("My favourite letter: %c\n", s.c);
return 0;
}
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Output

my favourite number 100

My favourite letter: z

 31. return

 In c programming, return is a keyword that ends or terminates a function and returns the desired output. When a function is ready to return the result to the function calling it, the return keyword is used.

 
#include <stdio.h>
void print_() // void method print_()
{
printf("Return Statement is executed");
}
int main() // main function of the program
{
print_(); // Calling print_() function
return 0;
}
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Example 

A program to demonstrate the use of return keyword in c 

#include <stdio.h> 

void print_() // void method print_()

Output

Return Statement is executed

32. auto 

auto is a keyword in c programming. Auto stands for automatic, which declares the variable automatically. An auto variable has the automatic storage duration the same as local variables.

Syntax of auto in c programming

auto int variable_name;

Here int is the data type of variable, and auto is the storage class that belongs to it. 

Example- 

 
#include<stdio.h>
int main()
{
auto int n = 5;
{
auto int n = 20;
printf(" num2 %d", n);
}
printf("\n");
printf("num1 %d", n);
return 0;
}
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Output

 num2 20

num1 5

Conclusion 

In a nutshell, all these keywords and their usage are essential in building great programming skills. This article will aid support to your c programming learning journey. 

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