I have a programme below:

************* filename: a.c ***************
#include<curses.h>
main()
{
initscr();
........
........ /* other code */
}
*******************************************

then I input the command: gcc a.c
there are a lot of errors like this: undefined reference to 'initscr'
But
the file "curses.h" is included in '/usr/include',
and,the procedure 'initscr()' is declared in file 'curses.h' this way:
extern NCURSES_EXPORT(WINDOW *) initscr(void);

Why this error happens?
How can I correct it?
My email is: wwnn1_class@sina.com
Thanks!

You need to link the curses library. Try compiling with the following command:

gcc -o programname code.c -lcurses

Usually curses is just a link to ncurses so if that doesn't work try ncurses instead.