Compilare: user.c: In function ‘check_number’: user.c:13:1: warning: implicit declaration of function ‘pow’ [-Wimplicit-function-declaration] if ((((number % (int)pow(10, i)) - (number % (int)pow(10, i-1)))/(int)pow(10, i-1) == 2) || (((number % (int)pow(10, i)) - (number % (int)pow(10, i-1)))/(int)pow(10, i-1) == 3) || (((number % (int)pow(10, i)) - (number % (int)pow(10, i-1)))/(int)pow(10, i-1) == 5) || (((number % (int)pow(10, i)) - (number % (int)pow(10, i-1)))/(int)pow(10, i-1) == 7)) ^ user.c:13:22: warning: incompatible implicit declaration of built-in function ‘pow’ [enabled by default] if ((((number % (int)pow(10, i)) - (number % (int)pow(10, i-1)))/(int)pow(10, i-1) == 2) || (((number % (int)pow(10, i)) - (number % (int)pow(10, i-1)))/(int)pow(10, i-1) == 3) || (((number % (int)pow(10, i)) - (number % (int)pow(10, i-1)))/(int)pow(10, i-1) == 5) || (((number % (int)pow(10, i)) - (number % (int)pow(10, i-1)))/(int)pow(10, i-1) == 7)) ^ user.c: At top level: user.c:27:1: warning: return type defaults to ‘int’ [enabled by default] main(){ ^ user.c: In function ‘check_number’: user.c:10:2: warning: ‘j’ may be used uninitialized in this function [-Wmaybe-uninitialized] j++; ^