C Tutorial

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Variables in C

A variable can be defined as a name allocated to a storage space that can be manipulated by our programs. Every variable in C arbitrates about the overall layout and the size occupied of the variable's memory, this statement reflects that each variable has a specific type. Also, it determines the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

A variable name consists of an individual character set or combination of character sets. In simple terms, the name of a variable can be composed of letters, digits, and a special character (underscore character).

Note: The variable name must begin with either a letter or an underscore.

The naming of variables in C is case-sensitive, i.e., the uppercase and lowercase letters are distinct.

By the above explanation, we get a basic idea about variables in C. To understand more about them, it is essential to learn various types of variables that exists in C. The basic variable types in C are as follows.

Sr.No.Variable Type Description
1int (Integer)   Stands for integer and it is a data type which is used for variable declarations or declaration of functions of different types
2float  Float is a data type which is used to represent floating point quantities or numbers. .  
3char  Typically, a single octet (one byte). It is an integer type
4doubleA double-precision floating point value.
5void  Represents the absence of type.  

In the C programming language, there exists a path which allows us (the programmer) to define various other types of variables. These types are Pointer, Array, Enumeration, Structure, Union, etc.


The keyword int in C programming stands for integer and it is a data type which is used for variable declarations or declaration of functions of different types. Similar to every other programming language, the C programming language also comes with types which are in-built to differentiate between various data (It can be either input or output or intermediate).

Int or Integer is a data type which is quoted as usual in every programming language. By usual we mean common data type. It is quoted as usual because of its wide usage or application in scientific computing or general programming.

In the C programming language, the integer type or the data of type integer is represented using the notation int. The various types or various variants of int are stated below.

  • int
  • long
  • short
  • long long

These types are differentiated based on the memory occupied by them. Each variant of int consumes different memory and it is discussed below using a tabular representation.

Variants of integer OR Integer Types in C

In order to understand the various integer types in C, it is important to look at the storage sizes of them and their value ranges. The following table provides these details in clear and concise manner.

Integer TypeSize (Storage size)Range (Value range)
int2 or 4 bytes-32,768 to 32,767 or -2,147,483,648 to 2,147,483,647
unsigned int2 or 4 bytes0 to 65,535 or 0 to 4,294,967,295
short2 bytes-32,768 to 32,767
unsigned short2 bytes0 to 65,535
long8 bytes or (4bytes for 32 bit OS)-9223372036854775808 to 9223372036854775807
unsigned long8 bytes0 to 18446744073709551615
char1 byte-128 to 127 or 0 to 255
unsigned char1 byte0 to 255
signed char1 byte-128 to 127
  • The size of signed and unsigned versions will be the same.
  • The size of int is equal to four bytes (4 bytes).
  • The size of short is less than or equal to the size of int.
  • The size of int is less than or equal to the size of long.
  • Hence, the size of long will be less than or equal to the size of long long.

Example :

#include <stdio.h> //header files

int main()
   int age;  // local variable of type int

   age = 25; // value of declared variable set to ‘25’
   printf("The entered value in variable age is %d .\n", age);

   return 0;

Program 1: Program to find the size of Int

#include <stdio.h> //header files
int main()
 int IntType; // local variable of type int
 printf("The size of int is: %ld\n", sizeof(IntType)); //prints the size of int
	return 0;

Float in C

Float is a data type which is used to represent floating point quantities or numbers (real numbers). Float requires 4 bytes of memory for their storage and its decimal digit precision is 6, i.e., number of digits after the fraction are 6.

Most C compilers follow the IEEE 754 standard for encoding the float values. According to this standard, the 32 bit single precision floating point number is represented as:

1 sign bit8 bits for exponent23 bits for significant(value)

Declaration of Float in C

Normally, the conversion character used with float is %f. The reserve word to declare a floating type variable is float and the syntax of float in C language is as follows,

float variable_name;

* The range of float lies between 1.17 x  to 3.4 x .

Program 2: Sum and product of of two floating numbers


void main( )
  float num1, num2, sum, product;  //floating variables declaration
  printf("Enter the first number: ");
  printf("Enter the second number: ");

   sum = num1+num2;    //calculating the sum of two numbers
   product = num1*num2;  //calculating the sum of two numbers

  printf("The Sum of two numbers = %f",sum);
  printf("\n The Product of two numbers = %f",product);
  getch( );

Char in C


Suppose there is an array of size 10 and we need to store a string “computer” inside it. This can be simply done using the following piece of code;

char a[10] = "computer";

When this piece of code is executed, an array of size 10 is created with string “computer” inside it which looks something like this;


Here, the ‘\0’ is used to indicate the end of a string.


#include<stdio.h>  // header files 
int main ()
    char string[15];  //declaring the local variables
    char *ptr;  //declaring the character pointer
    printf ("Please enter a character:\n");
    gets (string);
    puts (string);
    ptr = string;
    printf ("name = %c", *ptr);

Void in C

The term void in C programming means “no type”, “no value” or “no parameters”, depending on the context.

The use of void depending on the context, is used for:

  • a pointer does not have a specific type and could point to different types.
  • a function does not return value
  • a function does not accept parameters.

Advantages of using the Null Character in C

  • By using the NULL character or NULL byte, we can quickly check whether a value is null or not.
  • Generally in C, we can use any other type of variable instead of NULL, but using such might require an explicit or external comparison for a specific value.

Every time we come across a comparison where the result of the comparison is ‘0’ or zero, then there is a change in the status register. A flag is automatically set in the status register. This can be used in conditional instructions (used for comparisons), such as conditional jump.

  • Also, another advantage of using NULL is that it represents invalid value pointers.