Expression, Type Conversion and Preprocessor Directives

Expression in C

An expression in C is a combination of variables, constants, operators, and functions that are evaluated to produce a result.

Types of Expressions:

1. Arithmetic Expressions:
   • Use arithmetic operators (+, -, *, /, %).
   • Example: a + b - c.
2. Relational Expressions:
   • Compare values using relational operators (<, >, <=, >=, ==, !=).
   • Example: a > b.
3. Logical Expressions:
   • Combine conditions using logical operators (&&, ||, !).
   • Example: (a > b) && (b > c).
4. Bitwise Expressions:
   • Perform bitwise operations (&, |, ^, <<, >>).
   • Example: a & b.
5. Conditional Expressions:
   • Use the ternary operator (? :).
   • Example: result = (a > b) ? a : b.
6. Assignment Expressions:
   • Assign a value to a variable.
   • Example: a = b + c.

Type Conversion in C

Type conversion is the process of converting a variable from one data type to another.

Types of Type Conversion:

1. Implicit Type Conversion (Type Promotion):
   • Automatically performed by the compiler.
   • Converts smaller data types to larger ones (e.g., int to float).

Example:

int a = 5;
float b = a; // ‘a’ is automatically converted to float

        2. Explicit Type Conversion (Type Casting):

• Manually performed by the programmer using the cast operator (type).

Example:

float a = 5.5;
int b = (int)a; // ‘a’ is explicitly cast to int

Preprocessor Directives in C

Preprocessor directives are instructions processed by the preprocessor before the compilation of the program. They begin with a # symbol.

Types of Preprocessor Directives:

1. File Inclusion (#include):
   • Includes header files in the program.

Example: