//1. char 转 int
char a = '3';
int intA = a - '0';
//2.string 转 int
int num = atoi(input.data());
//3.num 转 string
string resultString = to_string(num);
//1. char 转 int
char a = '3';
int intA = a - '0';
//2.string 转 int
int num = atoi(input.data());
//3.num 转 string
string resultString = to_string(num);