An expression is anything that evaluates to a numeric value.
Simple Expression: The simplest C expression consists of a single item: a simple variable, literal constant, or symbolic constant. Ex .PI , 20 , rate , -1.25
Complex Expression:Complex expressions consist of simpler expressions connected by operators.

Ex: 2 + 8 1.25 / 8 + 5 * rate + rate * rate / cost

Types of ‘C’ Instructions:

• Declaration Instructions: Used to declare type of variable used in program.

Ex. int no; float grosssal; char code;

• Arithmetic Instructions: Used to perform some arithmetic function.

Ex: result = no1 + no2 ; k = 5 / 3;

• Control Instructions: Used to control sequence of execution of various program statements.
  1. Sequence control Instruction
  2. Selection or decision Instruction
  3. Repeating or loop Instruction
  4. Case control Instruction

Operators:
An operator is a symbol that instructs C to perform some operation, or action, on one or more operands.
An operand is something that an operator acts on.
Arithmetic Operators: +, -, *, /, %, ++, —

• Unary : ++ (Increment), — (Decrement)
• Binary : + , – ,* , / , %

Operators	Relative Precedence
++ —	1
* / %	2
+ –	3