===== *p =====
48
49
50
63
========== p ==========
012?
12?
2?
?
========== *p - '0' ==========
'0' -> 0
'1' -> 1
'2' -> 2
'?' -> 15
========== atoi(p) ==========
"012?" -> 12
"12?" -> 12
"2?" -> 2
"?" -> 0