Keywords in C: List of Keywords

auto

This keyword is used for automatic storage class, variables are created and initialized locally within blocks.

Example

auto int num = 5;

In the given example in the C Editor, an integer variable num is initialized to 5.

break

Used to terminate a loop or switch statement prematurely.

Example

for (int i = 0; i < 10; i++) {
 if (i == 5) {
 break;
 } }

In the provided example, the loop will stop when the value of i becomes 5.

case

Used in the switch statement to define different cases to be matched.

Example

switch (option) {
 case 1:
 // code for case 1
 break;
 case 2:
 // code for case 2
 break;
 default:
 // code for default case
}

char

Data type for storing a single character.

Example

char letter = 'A';

In the example, the character, “A” is assigned to the variable letter.

const

Used to define constants that cannot be modified after initialization.

Example

const int MAX_VALUE = 100;

In the given example, MAX_VALUE is a constant with a value of 100.

continue

Used to skip the rest of the loop body and proceed to the next iteration.

Example

for (int i = 0; i < 5; i++) {
 if (i == 2) {
 continue;
 }
 // code here will be skipped for i = 2
}

In the example, when i=2, the iteration is skipped and the next iteration with i=3 begins.

default

Used in the switch statement as the default case when no other cases match.

Example

switch (option) {
 case 1:
 // code for case 1
 break;
 default:
 // code for default case
}

do

Used to start a do-while loop, which guarantees the loop body executes at least once.

Example

do {
 // loop body
} while (condition);

double

Data type for storing double-precision floating-point numbers.

Example

double value = 3.14159;

In the example, the variable value is assigned the value 3.14159.

else

Used with if statements to define an alternative block of code to execute when the condition is false.

Example

if (x > 0) {
 // code when x is positive
} else {
 // code when x is non-positive
}

In this example, if the value of x is positive, a positive message is printed; otherwise, a non-positive message is printed using an if-else statement.

enum

Used to define an enumerated type consisting of named integer constants.

Example

enum Weekdays {
 MON, TUE, WED, THU, FRI, SAT, SUN
};

In the example, a set of weekdays is defined using an enum.

extern

Declares a variable or function as existing externally, often used when variables are defined in one file and used in another.

Example

extern int count;

In this example, an external variable named count is declared.

float

Data type for storing single-precision floating-point numbers.

Example

float value = 2.71828f;

In the example, the variable value is assigned the value 2.71828f.

for

Used to start a for loop, which repeats a block of code for a specified number of iterations.

Example

for (int i = 0; i < 10; i++) {
 // code to repeat
}

In this example, the loop iterates 10 times, printing the iteration index.

goto

Used to transfer control to a labeled statement in the same function.

Example

goto label;
// ...
label:
// statement to jump to

In this example, depending on whether x is positive or not, the program jumps to corresponding labels and prints messages using the goto statement.

if

Used to conditionally execute a block of code based on a specified condition.

Example

if (x > 0) {
 // code to execute when x is positive
}

In this example, it checks if x is positive and prints a message accordingly.

int

Data type for storing integer values.

Example

int num = 42;

In this example, an integer variable num is declared with a value and printed.

long

Data type for storing larger integer values.

Example

long largeNum = 1234567890L;

In this example, a long integer variable largeNum is declared with a value and printed.

register

Suggests to the compiler that a variable should be stored in a CPU register for faster access.

Example

register int counter = 0;

return

Used to exit a function and return a value to the caller.

Example

int add(int a, int b) {
 return a + b;
}

In this example, a function add()is defined that returns the sum of two integers.

short

Data type for storing smaller integer values.

Example

short smallNum = 32767;

In this example, a short integer variable smallNum is declared with a value and printed.

signed

Specifies that a variable can hold both positive and negative values.

Example

signed int temperature = -10;

sizeof

Returns the size, in bytes, of a data type or variable.

Example

int size = sizeof(int);

In this example, it calculates and prints the size of the int data type.

static

Declares a variable with static storage duration, retaining its value between function calls.

Example

static int counter = 0;

struct

Used to define a user-defined data type that groups variables of different types under a single name.

Example

struct Point {
 int x;
 int y;
};

In this example, a structure type Point is defined, an instance is created, and values are assigned.

switch

Used to evaluate a variable or expression against a set of possible values and execute the corresponding case.

Example

switch (option) {
 case 1:
 // code for case 1
 break;
 case 2:
 // code for case 2
 break;
 default:
 // code for default case
}

In this example in the C Compiler, the program executes code blocks based on the value of the option variable using a switch statement.

typedef

Used to create an alias for an existing data type, improving code readability.

Example

typedef unsigned long ulong;

In this example, it creates an alias ulong for the unsigned long data type and uses it.

union

Similar to a struct, a union allows storing different data types in the same memory location.

Example:

union Data {
 int iValue;
 float fValue;
};

unsigned

Specifies that a variable can hold only positive values.

Example

unsigned int count = 10;

In this example, an unsigned integer variable count is declared and its value is printed.

void

Represents the absence of a value or return type in functions.

Example

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

In this example, a function printMessage() is defined that prints a message.

volatile

Indicates that a variable can be changed by external entities, preventing certain compiler optimizations.

Example

volatile int sensorValue = 0;

while

Used to start a while loop, which repeats a block of code as long as a condition is true.

Example

while (x < 100) {
 // code to repeat while x < 100
}

In this example, the loop repeats while x is less than 100, printing x in each iteration.

Summary

The C keywords are essential language constructs with established meanings. Understanding these keywords is critical for error-free coding. Further, tokens include different aspects of C++ code like keywords, identifiers, constants, strings, special symbols, & operators, making them the core of C programs. For detailed theoretical and practical understanding, join our C Certification Course.