char prev;  // previous character
bool point = false; // check if there is a point in the number
char op[50];  // the operation
char rez[50];  // the result
int mode = 0;  // mode of operation
char x = '+';  // first operator
char y = '-';  // second operator
int ct = 0;  // character count 
int intrerupere = 0;  // active/inactive interrupt