What is the meaning of the GCC warning "case label value exceeds maximum value for type"?

Well, KEY_F(9) would be 273 (see curses.h) which exceeds the range of char (-128,127).

A char is a number between -128 and 127. KEY_F(9) probably is a value outside of that range.

Use:

• unsigned char, or
• int, or
• (char) KEY_F(9)

Or even better, use a debugger and determine sizeof(KEY_F(9)) to make sure it's a byte and not a short.

In this case, KEY_F(9) is evaluating to something outside the range of char. The switch statement is assuming that because its argument is a char, that all case labels will be also. Changing the switch to read switch((unsigned int)ch) will cure it.