In C programming, variables or memory locations should be declared before it can be used. Similarly, a function also needs to be declared before use.
This tutorial will focus on fundamental data types. To learn about derived data types, visit the corresponding tutorial.
Integers are whole numbers that can have both positive and negative values but no decimal values. Example: 0, -5, 10
In C programming, keyword int is used for declaring integer variable. For example:
Here, id is a variable of type integer.
You can declare multiple variable at once in C programming. For example:
int id, age;
The size of int is either 2 bytes(In older PC's) or 4 bytes. If you consider an integer having size of 4 byte( equal to 32 bits), it can take 232 distinct states as: -231,-231+1, ...,-2, -1, 0, 1, 2, ..., 231-2, 231-1. If you try to store larger number than 231-1, i.e,+2147483647 and smaller number than -231, i.e, -2147483648, program will not run correctly.
Similarly, int of 2 bytes, it can take 216 distinct states from -215 to 215-1.
Floating type variables can hold real numbers such as: 2.34, -9.382, 5.0 etc. You can declare a floating point variable in C by using either float or double keyword. For example:
float accountBalance; double bookPrice;
Here, both accountBalance and bookPrice are floating type variables.
In C, floating values can be represented in exponential form as well. For example:
float normalizationFactor = 22.442e2;
The size of float (single precision float data type) is 4 bytes. And the size of double (double precision float data type) is 8 bytes. Floating point variables has a precision of 6 digits whereas the precision of double is 14 digits.
Keyword char is used for declaring character type variables. For example:
char test = 'h';
Here, test is a character variable. The value of test is 'h'.
The size of character variable is 1 byte.
Qualifiers alters the meaning of base data types to yield a new data type.
Size qualifiers alters the size of a basic type. There are two size qualifiers, long and short. For example:
long double i;
The size of double is 8 bytes. However, when long keyword is used, that variable becomes 10 bytes.
Learn more about long keyword in C programming.
There is another keyword short which can be used if you previously know the value of a variable will always be a small number.
Integers and floating point variables can hold both negative and positive values. However, if a variable needs to hold positive value only, unsigned data types are used. For example:
// unsigned variables cannot hold negative value unsigned int positiveInteger;
There is another qualifier signed which can hold both negative and positive only. However, it is not necessary to define variable signed since a variable is signed by default.
An integer variable of 4 bytes can hold data from -231 to 231-1. However, if the variable is defined as unsigned, it can hold data from 0 to 232-1.
It is important to note that, sign qualifiers can be applied to int and char types only.
An identifier can be declared as a constant. To do so const keyword is used.
const int cost = 20;
The value of cost cannot be changed in the program.
A variable should be declared volatile whenever its value can be changed by some external sources outside the program. Keyword volatile is used for creating volatile variables.