How to use Macros??

Hey peoples im new to macros and i have seem to have gotten the notation for my VOLUME macro, however i dont know what to do for the PRINTSTR macro which is supposed to ask a string for you to input which will then be outputted onto the next line.

Code:

#include <stdlib.h>
#include <stdio.h>

int main()
{
   #define VOLUME(r) ((4.0 /3) * 3.14 * (r)*(r)*(r))
   #define PRINTSTR(str) printf("%s")
   char str[100];
   float r;

   printf("Please enter the radius of a sphere \n");
   scanf("%f", &r);
   printf("The volume of the sphere is: %.2f\n", VOLUME(r));
   printf("Enter a string you want to print \n");
   scanf("%s", str);
   PRINTSTR(str);
   return 0;
}

You went wrong into the printf function, replace it with:

Code:

#define PRINTSTR(str) printf("%s", str);

Whenever you have doubts in the macro just give

Code:

 
 gcc -E filename.c 

may be gcc or cc

This will show you how the macros are expanded

This gets tedious on most files as the preprocessor also includes everything. Checking the macros and warnings is enough most of the time.