test.cc:50: warning: comparison is always false due to limited range of data range?

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I have...

    char c = getch ();
        if (c == KEY_F(1))
        {
            char pulsa[]="Pulsa F1 para continuar...";
            mvwprintw(win,(maxx+4),(maxx-strlen(pulsa))/2,"%s",pulsa);
        }

when I try to compile I see this error...
test.cc:50: warning: comparison is always false due to limited range of data 
range

I am using this headers, maybe here is the error:
#include <iostream>
#include <ncurses.h>
#include <string.h>
#include <stdlib.h> // exit()

What's wrong?
I am copy the code from ncurses howto.