C 的入门者请进，否则不要花时间click

只需要把下面代码paste到new project, run, 即看到效果

// Feb 4th, 2002

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

double foo(int a,double *b);

int main(void)
{

double y=0,z=0;
printf("\n0.....y Address = %p\n",&y); // print y address
z=foo(3,&y); //Square; if 3, return z=9; if 4, z=16...
printf("\nz = 3*y = %2.0f\n",z);

return 0;
}

double foo(int a,double *b)
{
printf("1.....pAddress(b) = %p, double value(*b) = %f\n",b,*b);
*b=a;
(*b) *= *b; //Square; if a=3, return 9;
printf("(*b) *= *b;\n");

//b=b 1; //[NO] make b to another address;
//*b=*b 1; //[YES] value itself 1;
/*
double k = 2;
printf("1.1...pAddress(&k) = %p\n",&k);
b=&k; //[YES] if b= sth's address;
// *b= sth's value;
printf("b = &k;\n");
printf("2.....pAddress(b) = %p, double value(*b) =%f\n\n",b,*b);
*/

return *b;

//return b; // [NO] cannot convert from 'double *' to 'double'
//return (*b)*(*b); // works also

}