Explain the differences between macros and subroutines.

Macros Vs Subroutines

(i) Macros are pre-processor directives which are processed before the source program is passed to the compiler.

Subroutines are blocks of codes along with a exact task, to be performed and are directly passed to the compiler.

(ii) In a macro call the pre-processor replaces the macro template along with its macro expansion, in a literal manner.

As against this, into a function call the control is passed to a function with exact arguments, some computations are performed in the function and a helpful value is returned back from the function.

(iii) Macro raises the program size. For illustration, if we use a macro hundred times in a program, the macro expansion goes in our source code at hundred various places. Because the function makes the program smaller and compact, for example, if a function is used, the even if this is called from hundred various places in the program, this would take similar amount of space in the program.

(iv) Macros compose the program run faster as they have already been expanded and placed into the source code before compilation. While, passing arguments to a function and obtaining back the returned values does take time and would thus slow down the program.

(v)   Illustration of macro

#define AREA(x) (3.14*x*x) // macro definition main(){

float r1=6.25, r2=2.5, a;

a=AREA(r1); // expanded to (3.14 * r1 * r1)

printf("\n Area of circle =%f",a);

a=AREA(r2); // // expanded to (3.14 * r2 * r2)

printf("\n Area of circle= %f",a);} Example of subroutine

main(){

float r1=6.25, r2=2.5, a;

a=AREA(r1); // calls AREA() printf("\n Area of circle =%f",a); a=AREA(r2); // calls AREA()

printf("\n Area of circle= %f",a);}

float AREA(float r) // subroutine{

return 3.14*r*r;}