Compilare: user.c: In function ‘main’: user.c:24:13: warning: implicit declaration of function ‘exit’ [-Wimplicit-function-declaration] exit(1); ^ user.c:24:13: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] user.c:101:17: warning: incompatible implicit declaration of built-in function ‘exit’ [enabled by default] exit(1); ^ user.c:17:9: warning: unused variable ‘a’ [-Wunused-variable] int a=1; ^