I want to exchange pointer values, but it doesn't work and I'm stumbled
I would be grateful if you could give me a recommended reference book that describes how to use the pointer
It would be helpful if you could give me advice on the code

code
#include<stdio.h>
int input_int (int * pd);
void swap_int (int * pdata1, int * pdata2);
int main (void)
{
    int data1, data2;
    while (input_int (&data1)! = EOF&&input_int (&data2)! = EOF) {
        printf ("** Before exchange ** \ n");
        printf ("data1 =% d \ n", data1);
        printf ("data2 =% d \ n", data2);
        swap_int (&data1,&data2);
        printf ("** After exchange ** \ n");
        printf ("data1 =% d \ n", data1);
        printf ("data2 =% d \ n", data2);
        printf ("\ n");
    }
    return 0;
}

void swap_int (int * pdata1, int * pdata2)
{
  int tmp;
    tmp = * pdata1;
    * pdata1 = * pdata2;
    * pdata2 = tmp;

    printf ("Input num:");
    return scanf ("% d% d",&* pdata1,&* pdata2);


}

Error details
swpint.c: In function 'swap_int':
swapint.c: 48: 10: warning: 'return'with a value.in function returning void
return scanf ("% d% d",&* pdata1,&* pdata2);
swapint.c38: 6note: declared here
void swap int (int * pdata, int * pdata2)
Is the error message

The execution image is
input num: 10
input num: 20
** Before replacement **
data1 = 10
data2 = 20
** After exchange **
data1 = 20
data2 = 10
Execution image when it can be executed