What Is Micro Substitution

The #define directive is the most common processor directive, which tell the Processor to replace every occurrence of a particular character string ( that is, a macro name ) with a specified value ( that is, macro body).

The syntax for the #define directive is:

 #define Macro_name macro_body

Here macro name is an identifier that can contain letters, numerals, or underscores. Macro_body may be a string  or a data item, which is used to substitute each macro_name found in the program. As mentioned earlier, the operation to replace occurrences of the macro_ name with the value specified by the macro_ body is known as macro substitution or macro expansion. The value in the macro body specified by a #define directive can be any.character string or number.

Example: #define NAME  "to more"

Here NAME will be replaced by "to more." .

Other examples:

#define MUX  (8*8)

On the other hand, we can use #undef directive to remove the definition of a macro name who has been previously defined.


 #undef macro_name

Here macro_name is an identifier that has been previously defined by a #define directive.The #undef directive "undefined" a macro name.For instance the following segment of code.

#define NAME "author"

printf(" I am of %s.\n ",NAME);
#undef NAME 

It defines the macro name NAME first, and uses the macro name for the print( function  then it removes the macro name.

Defining the macro with arguments:
You can specify one or more arguments to a macro name defined by the #define directive, so that the macro name can be treated like a simple function that accepts arguments.

 #define MUL(val1,val2) ((val1)*(val2))

When the following statement.

 A result= MUL(2,3)+10;

The  preprocessor substitute the expression 2 for val1 and 3 for val2  and the produces the following statement.


/*Program to understand macros with arguments*/

#include <studio.h>
#define SUM(x,y) ((x)+(y))
#define PROD(x,y) ((x)+(y))

     int l,m,i,j,a=5,b=3;
     float p,q;


Output :



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