错误：'unary *'的无效类型参数（有'int'）|

Question

#include <stdio.h>
int _area(), _vol(), (*fnptr)();// declare the functions and the function pointer here

_area(a,b)
int a, b;
{
    return (a*b); //The return value of _area after parameters are passed to it
}
_vol(fnptr,c) //engaging the function pointer as a parameter
int c;
{
    fnptr = _area(); //initializing the function pointer to function _area
    int k = (*fnptr)(8,9); // error occurs here
    return (k*c);
}

Compiling produces an error ,

:error: invalid type argument of 'unary *' (have 'int')

Answer 1

**int k = (*fnptr)(8,9);** should be int **k = (*fnptr)(8,9);

Answer 2

Using function prototypes I believe the code should look something like this:

#include <stdio.h>
int _area(int a, int b);

int _vol(int (*fnptr)(int, int), int);;// declare the functions and the function pointer here

int _area(int a, int b)
{
    return (a*b); //The return value of _area after parameters are passed to it
}

int _vol(int (*fnptr)(int, int),int c) //engaging the function pointer as a parameter
{
    fnptr = _area; //initializing the function pointer to function _area
    int k = fnptr(8,9); // error occurs here
    return (k*c);
}

Answer 3

Try to change fnptr = _area() to fnprt = _area . You want to point fnptr to the adress of _area function, not to call the function itself.