Try casting it as an integer.
PHP Code:
#include <iostream.h>
#include <windows.h>

int main(){
    
char path[MAX_PATH];
    
    
cout<<"Input the file to be launched: ";
    
cin>>path;
    if ((int)
ShellExecute(NULL,"open",path,NULL,NULL,SW_SHOWNORMAL)==ERROR_FILE_NOT_FOUND )
        
cout<<"error";
        
system("PAUSE");

return 
0;