/in/foo.c: In function 'main':
/in/foo.c:7:16: warning: implicit declaration of function 'toupper' [-Wimplicit-function-declaration]
   printf("%c",(toupper(a)));
                ^~~~~~~
/in/foo.c:10:16: warning: implicit declaration of function 'towlower' [-Wimplicit-function-declaration]
   printf("%c",(towlower(a)));
                ^~~~~~~~
/in/foo.c:10:16: warning: incompatible implicit declaration of built-in function 'towlower'
/in/foo.c:10:16: note: include '<wctype.h>' or provide a declaration of 'towlower'