The data in C can be classified into four types.

• Basic type: These are the arithmetic data type. These are further classified into two groups- integer type data and floating-point type data.
• Enumerated type: These data are arithmetic data which are used to define variables which can only assign discrete integer values in the program.
• Void type: The void indicates that there is no value available.
• Derived data: derived data includes- array, pointer, structure, function and union types of data.

Variables

Variables are the name given to the storage area that can be manipulated by the programs. The variables are of specific type, which establishes the layout and size of memory of the variable. Variable names can contain digits, letters and underscore characters however it must start with an underscore or a letter. As c is case sensitive, uppercase and lowercase letters are distinct. Some basic types of variables are int, char, double, float and void.

The variable definition commands the compiler how much storage is required to create the variable and where it will be stored.

The variable declaration tells the compiler that a variable exists with the given name and type, so that the compiler can continue to compile without requiring all details about the variable.

Constants And Literals

The fixed values which are not altered during the execution of a program are referred to as constants. Constants are also known as literals. Constants can be of any data type such as a floating constant, an integer constant, a character constant etc. constants are similar to the regular variables except the fact that their values cannot be changed once they are already defined.

Operators

Operators are the symbols that command the compiler to perform specific logical and mathematical functions. C language has the following types of operators that are used in writing the program statements.

• Relational operators: ==, !=, >, <, >=, <=
• Arithmetic operators: +, -, *, /, %, ++, —
• Bitwise operators: &, |, <<, >>
• Logical operators: &&, ||, !
• Misc operators: sizeof(), &, *, ? :
• Assignment operators: =, +=, -=, *=, /=, %=, <<=, >>=, &=, |=

Decision Making

Decision-making structures are structures that are the conditions that are specified by the programmers along with the statements so that they are evaluated by the programs to determine whether the statement is true or false. A typical decision making structure is given below:

• If…else statement
• Nested if statement
• Switch statement
• Nested switch statement