format MS COFF
public  _power as 'power'

include 'C:\FASM\INCLUDE\WIN32A.INC'


section '.text' code readable executable

proc _power
     push ebp
    mov ebp,esp

     mov eax,[ebp+4]
     mov ebx,[ebp+8]
     mul eax

 pop ebp
     ret
endp


    

using namespace std;
extern int power(int,int);


int main(){
        int a=10,b=10;
      std::cout<<power(a,b)<<endl;
    getchar();
}

    

public  power as '_power'  ; Mangle exported name, not an internal one.
and in main.cpp:
#include <iostream>
and
extern "C" int power(int,int);
    

...
        mov eax,[ebp+8]  ;first parameter
        mov ebx,[ebp+12] ;second parameter
...    

...
        mov edx,[ebp+12] ;second parameter, ebx should not be altered for C interface
        mul edx  ;edx:eax=eax*edx
...