Keywords / Reserve Words

 • Keywords are predefined, reserved words used in programming that have special meanings to the compiler.



 

Identifiers

• An identifier in C consists of a sequence of letters, digits, or underscore characters.

• Identifiers are set when you declare variables, arrays, enumerations, structures, union, typedef and functions.

 Rules

▫ A valid identifier can have letters (both uppercase and lowercase letters), digits and underscores.

▫ The first letter of an identifier should be either a letter or an underscore.

▫ However, it is discouraged to start an identifier name with an underscore.

▫ There is no rule on length of an identifier.

▫ However, the first 31 characters of identifiers are discriminated by the compiler.

 

Variables

• The rules for forming variable names:

▫ They must begin with a letter or underscore (_) and can be followed by any combination of letters (upper or lowercase), underscores, or the digits 0–9.

• Now we know that, variables are placeholders used to store values.


 

Data Types & Constants

• In C, any number, single character, or character string is known as a constant.

• There are five different types of constants available in C programming language;

▫ Integer constants

▫ Floating point constants

▫ Character constants

▫ Character String Constants

▫ Enumeration Constants


 

Constant Expression

• Expressions consisting entirely of constant values are called constant expressions.

eg - 128 + 7 – 17 

 

Statements

• A program statement is any valid expression (usually an assignment or function call) that is immediately followed by a semicolon, or it is one of the special statements like compound, statement, break, continue, do, for , go to, if, return, switch, while and null statement.

 

Variable Declaration

 • Declaration is done by simply listing the variables before the terminating semicolon of the definition.

• You can declare multiple variables in same type using a single statement




 Assigning Values to Variables

• After declaring a variable with a type, you can add some content or value to that variable.

 

• There are two ways to assign value to a variable:

▫ Assign the value directly in the program.

 ▫ Ask from user to input a value and then assign that value.