Keywords in C

Keywords in C are reserved words that have predefined meanings and are part of the C language syntax. These keywords cannot be used as variable names, function names, or any other identifiers within the program except for their intended purpose. They are used to define the structure flow and behavior of a C program.

The compiler recognizes a defined set of keywords in the C programming language. These keywords have specialized purposes and play critical roles in establishing the logic and behavior of a program. Here are some characteristics of C keywords:

Reserved: The C language reserves keywords are those keywords that cannot be used as identifiers in programs. Using a keyword as a variable name or other identifier will cause a compilation error.
Predefined Meaning: Each keyword has a specific meaning that is assigned by the C language. These meanings are built into the C language's grammar and syntax and the compiler interprets them accordingly.
Specific Use: Keywords are designed for specific purposes and contexts within the C language. They define control structures, data types, flow control, and other language constructs. Attempting to use a keyword outside of its intended purpose will result in a compilation error.
Standardized: C language keywords are standardized across different compilers and implementations. It ensures the consistency and portability of C programs across different platforms and environments.

A list of 32 keywords in the c language is given below:

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

Here is a brief explanation of each keyword in the C language along with their syntax and an example:

auto: This keyword declares an automatic variable with a local scope.

Syntax:

It has the following syntax:

Example:

Code:

#include <stdio.h>

int main() {
    auto int count = 10;
printf("Count: %d\n", count);

    {
        auto int count = 5;
printf("Inner Count: %d\n", count);
    }

printf("Count: %d\n", count);

    return 0;
}

Output:

Count: 10
Inner Count: 5
Count: 10

break: It is used to terminate the execution of a loop or switch statement.

Syntax:

It has the following syntax:

Code:

#include <stdio.h>

int main() {
    for (inti = 0; i< 10; i++) {
        if (i == 5) {
            break;
        }
printf("%d ", i);
    }

    return 0;
}

Output:

0 1 2 3 4

case: It is used in a switch statement to define different cases.

Syntax:

It has the following syntax:

Code:

#include <stdio.h>

int main() {
int choice = 2;
    switch (choice) {
        case 1:
printf("You chose option 1.\n");
            break;
        case 2:
printf("You chose option 2.\n");
            break;
        default:
printf("Invalid choice.\n");
    }

    return 0;
}

Output:

You chose option 2.

char: This keyword is used to declare a character data type.

Syntax:

It has the following syntax:

Example:

Code:

#include <stdio.h>

int main() {
    char grade = 'A';
printf("Grade: %c\n", grade);

    return 0;
}

Output:

Grade: A

const: It is used to declare constants, whose values cannot be modified.

Syntax:

It has the following syntax:

Code:

#include <stdio.h>

int main() {
constint MAX_SIZE = 100;
printf("Max Size: %d\n", MAX_SIZE);

    return 0;
}

Output:

Max Size: 100

continue: It is used to skip the remaining statements in a loop and continue with the next iteration.

Syntax:

It has the following syntax:

Code:

#include <stdio.h>

int main() {
    for (inti = 0; i< 10; i++) {
        if (i == 5) {
            continue;
        }
printf("%d ", i);
    }

    return 0;
}

Output:

0 1 2 3 4 6 7 8 9

default: It is used in a switch statement as the default case when no other cases match.

Syntax:

It has the following syntax:

Code:

#include <stdio.h>

int main() {
int choice = 3;
    switch (choice) {
        case 1:
printf("You chose option 1.\n");
            break;
        case 2:
printf("You chose option 2.\n");
            break;
        default:
printf("Invalid choice.\n");
    }

    return 0;
}

Output:

Invalid choice.ax: default:

do: It is used to create a do-while loop, which executes a block of code repeatedly until a condition is met.

Syntax:

It has the following syntax:

do {
    // code to be executed
} while (condition);

Code:

#include <stdio.h>

int main() {
inti = 0;
    do {
printf("%d ", i);
i++;
    } while (i< 5);

    return 0;
}

Output:

0 1 2 3 4

double: This keyword is used to declare a double-precision floating-point data type.

Syntax:

It has the following syntax:

Example:

Code:

#include <stdio.h>

int main() {
    double pi = 3.14159;
printf("Pi: %lf\n", pi);

    return 0;
}

Output:

Pi: 3.141590

else: It is used in an if statement to specify the block of code to be executed when the condition is false.

Syntax:

It has the following syntax:

if (condition) {
    // code to be executed if the condition is true
} else {
    // code to be executed if the condition is false
}

Code:

#include <stdio.h>

int main() {
int age = 20;
    if (age >= 18) {
printf("You are an adult.\n");
    } else {
printf("You are not an adult.\n");
    }

    return 0;
}

Output:

You are an adult.

enum: It is used to define an enumeration, which is a set of named values.

Syntax:

It has the following syntax:

enum enum_name {
    value1,
    value2,
    //...
};

Code:

#include <stdio.h>

enum Days {
    Monday,
    Tuesday,
    Wednesday,
    Thursday,
    Friday,
    Saturday,
    Sunday
};

int main() {
enum Days today = Tuesday;
printf("Today is day number %d\n", today);

    return 0;
}

Output:

Today is day number 1

extern: It is used to declare a variable or function that is defined in another file or external to the current scope.

Syntax:

It has the following syntax:

Code:

#include <stdio.h>

extern int global_variable;

int main() {
global_variable = 10;
printf("Global variable: %d\n", global_variable);

    return 0;
}

int global_variable;

Output:

Global variable: 10

float: This keyword is used to declare a single-precision floating-point data type.

Syntax:

It has the following syntax:

Example:

Code:

#include <stdio.h>

int main() {
    float weight = 65.5;
printf("Weight: %.2f\n", weight);

    return 0;
}

Output:

Weight: 65.50

for: It is used to create a for loop, which repeatedly executes a block of code based on a specified condition.

Syntax:

It has the following syntax:

for (initialization; condition; increment/decrement) {
    // code to be executed
}

Example:

for (int i = 0; i< 5; i++) {
printf("%d ", i);
}

Code:

#include <stdio.h>

int main() {
    for (inti = 0; i< 5; i++) {
printf("%d ", i);
    }
printf("\n");

    return 0;
}

Output:

0 1 2 3 4

goto: It is used to transfer control to a labeled statement within the same function.

Syntax:

It has the following syntax:

Code:

#include <stdio.h>

int main() {
    for (inti = 0; i< 10; i++) {
        if (i == 5) {
goto end;
        }
printf("%d ", i);
    }

    end:
printf("Loop ended.\n");

    return 0;
}

Output:

0 1 2 3 4
Loop ended.

if: It is used to create an if statement to perform a certain action based on a condition.

Syntax:

It has the following syntax:

if (condition) {
    // code to be executed if the condition is true
}

Code:

#include <stdio.h>

int main() {
int x = 5;
    if (x > 0) {
printf("x is a positive number.\n");
    }

    return 0;
}

Output:

x is a positive number.

int: This keyword is used to declare an integer data type.

Syntax:

It has the following syntax:

Example:

Code:

#include <stdio.h>

int main() {
int number = 10;
printf("Number: %d\n", number);

    return 0;
}

Output:

Number: 10

long: This keyword is used to declare a long integer data type.

Syntax:

It has the following syntax:

Example:

Code:

#include <stdio.h>

int main() {
    long population = 1000000;
printf("Population: %ld\n", population);

    return 0;
}

Output:

Population: 1000000

register: It is used to declare a register variable, which suggests the compiler to store the variable in a register for faster access.

Syntax:

It has the following syntax:

Example:

Code:

#include <stdio.h>

int main() {
    register intreg_var = 5;
printf("Register Variable: %d\n", reg_var);

    return 0;
}

Output:

Register Variable: 5

return: It is used to exit a function and return a value (if any) to the calling code.

Syntax:

It has the following syntax:

Code:

#include <stdio.h>

int square(intnum) {
    return num * num;
}

intmain() {
int result = square(5);
printf("Square: %d\n", result);

    return 0;
}

Output:

Square: 25

short: This keyword is used to declare a short integer data type.

Syntax:

It has the following syntax:

Code:

#include <stdio.h>

int main() {
    short temperature = -10;
printf("Temperature: %d\n", temperature);

    return 0;
}

Output:

Copy code
Temperature: -10

signed: It is used to declare a signed data type, which can represent both positive and negative values.

Syntax:

It has the following syntax:

Example:

Code:

#include <stdio.h>

int main() {
    signed int balance = -100;
printf("Balance: %d\n", balance);

    return 0;
}

Output:

Balance: -100

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

Syntax:

It has the following syntax:

Code:

#include <stdio.h>

int main() {
int size = sizeof(int);
printf("Size of int: %d bytes\n", size);

    return 0;
}

Output:

Size of int: 4 bytes

static: It is used to declare a variable or function that retains its value or scope even after the block in which it is defined has exited.

Syntax:

It has the following syntax:

static data_type variable_name;
static return_type function_name(arguments);

Code:

#include <stdio.h>

void increment() {
    static int count = 0;
    count++;
printf("Count: %d\n", count);
}

int main() {
increment();
increment();

    return 0;
}

Output:

Count: 1
Count: 2

struct: It is used to define a user-defined data type called a structure, which can hold multiple variables of different data types.

Syntax:

It has the following syntax:

struct struct_name {
data_type member1;
data_type member2;
    //...
};

Code:

#include <stdio.h>
#include <string.h>

struct Person {
    char name[20];
int age;
};

int main() {
struct Person student;
strcpy(student.name, "John");
student.age = 20;
printf("Name: %s, Age: %d\n", student.name, student.age);

    return 0;
}

Output:

Name: John, Age: 20

switch: It is used to create a switch statement, which allows multiple execution paths based on different cases.

Syntax:

It has the following syntax:

switch (expression) {
    case constant1:
        // code to be executed if expression matches constant1
        break;
    case constant2:
        // code to be executed if expression matches constant2
        break;
    //...
    default:
        // code to be executed if expression does not match any constant
}

Code:

#include <stdio.h>

int main() {
int choice = 2;
    switch (choice) {
        case 1:
printf("You chose option 1.\n");
            break;
        case 2:
printf("You chose option 2.\n");
            break;
        default:
printf("Invalid choice.\n");
    }

    return 0;
}

Output:

You chose option 2.

typedef: It is used to create a new name (alias) for an existing data type.

Syntax:

It has the following syntax:

Code:

#include <stdio.h>

typedef int marks;

int main() {
    marks math_marks = 95;
printf("Math Marks: %d\n", math_marks);

    return 0;
}

Code:

Math Marks: 95

union: It is used to define a user-defined data type called a union, which can hold different data types but only one member at a time.

Code:

#include <stdio.h>

union Number {
int integer;
    float floating_point;
};

int main() {
    union Number num;
num.integer = 10;
printf("Integer: %d\n", num.integer);

    return 0;
}

Output:

Integer: 10

unsigned: It is used to declare an unsigned data type, which can represent only positive

Syntax:

It has the following syntax:

Code:

#include <stdio.h>

int main() {
    unsigned int count = 100;
printf("Count: %u\n", count);

    return 0;
}

Output:

Count: 100

void: This keyword is used to indicate the absence of a specific type or to define functions that do not return a value.

Syntax:

It has the following syntax:

For function return type: void function_name(arguments);
As a data type: void variable_name;

Code:

#include <stdio.h>

void printMessage() {
printf("Hello, World!\n");
}

int main() {
printMessage();

    return 0;
}

Output:

Hello, World!

volatile: It is used to declare a variable that can be modified externally and should not be optimized by the compiler.

Syntax:

It has the following syntax:

Example:

volatile int sensor_reading;
// Access and modify the sensor_reading variable in an interrupt service routine

Code:

#include <stdio.h>

int main() {
    volatile int sensor_reading = 0;

    // Simulating sensor reading update
    for (inti = 0; i< 10; i++) {
sensor_reading = i;
printf("Sensor Reading: %d\n", sensor_reading);
    }

    return 0;
}

Output:

Sensor Reading: 0
Sensor Reading: 1
Sensor Reading: 2
Sensor Reading: 3
Sensor Reading: 4
Sensor Reading: 5
Sensor Reading: 6
Sensor Reading: 7
Sensor Reading: 8
Sensor Reading: 9

while: It is used to create a while loop, which repeatedly executes a block of code based on a specified condition.

Syntax:

It has the following syntax:

while (condition) {
    // code to be executed
}

Code:

#include <stdio.h>

int main() {
inti = 0;
    while (i< 5) {
printf("%d ", i);
i++;
    }
printf("\n");

    return 0;
}

Output:

0 1 2 3 4

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