switch, case and default:-

The switch and case statement is used when a block of statements has to be executed among many blocks. For example:
switch(expression)
{
    case '1':
    //some statements to execute when 1
    break;
    case '5':
    //some statements to execute when 5
    break;
    default:
    //some statements to execute when default;
}
Visit C switch statement to learn more.

char:-

The char keyword declares a character variable. For example:
char alphabet;
Here, alphabet is a character type variable.
To learn more, visit C data types.

const:-

An identifier can be declared constant by using const keyword.
const int a = 5;
To learn more, visit C variables and constants.

do...while

int i;
do 
{
   print("%d ",i);
   i++;
}
while (i<10)
To learn more, visit C do...while loop

double and float:-

Keywords double and float are used for declaring floating type variables. For example:
float number;
double longNumber;
Here, number is single precision floating type variable whereas, longNumber is a double precision floating type variable.
To learn more, visit C data types.

if and else:-

In C programming, if and else are used to make decisions.
if (i == 1)
   printf("i is 1.")
else
   prinf("i is not 1.")
If value of i is other than 1, output will be :
i is not 1
To learn more, visit C if...else statement.

enum:-

Enumeration types are declared in C programming using keyword enum. For example:
enum suit
{
    hearts;
    spades;
    clubs;
    diamonds;
};
Here, a enumerated variable suit is created having tags: hearts, spades, clubs and diamonds.
To learn more, visit C enum.

extern:-

The extern keyword declares that a variable or a function has external linkage outside of the file it is declared.
To learn more, visit C storage type.

for:-

There are three types of loops in C programming. The for loop is written in C programming using keyword for. For example:
for (i=0; i< 9;++i)
{
  printf("%d ",i);
}
Output
0 1 2 3 4 5 6 7 8
To learn more, visit C for loop.

goto:-

The goto keyword is used for unconditional jump to a labeled statement inside a function. For example:
for(i=1; i<5; ++i)
{
    if (i==10)
    goto error;
}
printf("i is not 10");
error:
    printf("Error, count cannot be 10.");
Output
Error, count cannot be 10.
To learn more, visit C goto.

int

The int keyword declares integer type variable. For example:
int count;
Here, count is a integer variable.
To learn more, visit C data types.

short, long, signed and unsigned:-

The short, long, signed and unsigned keywodrs are type modifiers that alters the meaning of a base data type to yield a new type.
short int smallInteger;
long int bigInteger;
signed int normalInteger;
unsigned int positiveInteger;
Range of int type data types
Data typesRange
short int-32768 to 32767
long int-2147483648 to 214743648
signed int-32768 to 32767
unsigned int0 to 65535

return:-

The return keyword terminates the function and returns the value.
int func()
{
    int b = 5;
    return b;
}
This function func() returns 5 to the calling function. To learn more, visit C user-defined functions.

sizeof:-

The sizeof keyword evaluates the size of data (a variable or a constant).
#include <stdio.h>
int main()
{
    printf("%u bytes.",sizeof(char));
}
To learn more, visit C operators.
Output
1 bytes.

register:-

The register keyword creates register variables which are much faster than normal variables.
register int var1;

static:-

The static keyword creates static variable. The value of the static variables persists until the end of the program. For example:
static int var;

struct:-

The struct keyword is used for declaring a structure. A structure can hold variables of different types under a single name.
struct student{
    char name[80];
     float marks;
     int age;
}s1, s2;
To learn more, visit C structures.

typedef

The typedef keyword is used to explicitly associate a type with an identifier.
typedef float kg;
kg bear, tiger;

union

A Union is used for grouping different types of variable under a single name.
union student 
{
    char name[80];
    float marks;
    int age;
}
To learn more, visit C unions.

void

The void keyword indicates that a function doesn't return any value.
void testFunction(int a)
{
  .....
}
Here, function testFunction( ) cannot return a value because the return type is void.

volatile

The volatile keyword is used for creating volatile objects. A volatile object can be modified in an unspecified way by the hardware.
const volatile number
Here, number is a volatile object.
Since, number is a constant variable, the program cannot changeit. However, hardware can change it since it is a volatile object.
Thankyou