An expression is a combination of variables, constants and operators arranged according to the syntax of the language. 

C can handle any complex expression with ease. 

It is little bit different from algebraic expression. 

Algebraic Expressions 
C Expressions 
axbcxd 
a*bc*d 
(m+n)(a+b) 
(m+n)*(a+b) 


Evaluation of expression: 

We can evaluate an expression by using assignment statement. As 

Variable = Expression. 

e.g. : 

Temp = ((f * cos(x)/sin (y))+(g * sin(x)/cos(y))) 

All relevant variables must be assigned values before the evaluation of the expression. 

Type conversion in expression: 

To effectively develop C programs, it would be necessary for you to understand the rules that are used for the implicit conversion of operands. 

If an expression contains an operation between an int and a float, the int would be automatically promoted to a float before carrying out of operation. 