C language Review (2) macro definition and Conditional compilation

Macro definition:
#Define g 9.8

.....

......

# UNDEFG

Macro-Defined Scope

Note:

# Define AB (x) x * X-2 * x + 10

AB (1 + 2) = 1 + 2*1 + 2-2*1 + 2 + 10 = 15

AB (3) = 3*3-2*3 + 10 = 13

AB (3) * 10 = 3*3-2*3 + 10*10 = 103

 

# Define AB (x) * (x)-2 * (x) + 10)

AB (1 + 2) = (1 + 2) * (1 + 2) + 10 = 13

AB (3) * 10 = (3*3-2*3 + 10) * 10 = 130

 

Macro is just a simple replacement of characters. Macro expansion is performed before compilation, and no memory units are allocated during expansion. The macro does not have a type problem. The macro name does not have a type. Its parameters are of no type. It is just a symbol. You can include the specified string when expanding.

Conditional compilation:

# Define debug

# Ifdef debug

....

# Else

......

# Endif

# If

# Else

# Endif