how can i use F1-F12 in switch case statement??

Depends on the operating system. Here is one thread you might want to read.

how can i use F1-F12 in switch case statement??

Write a program that inputs keystrokes, then displays the values entered in HEX.

But standard C cannot input function keys, so you may be out of luck. It all depends on the compiler you are using or how much you want to tap into the system APIs.

Some MS-Windows compilers support conio.h and getch() that will let you access special keys.

Ncurses?