In the database, the mobile phone number is of char type (1 1), and the bank card is stored of string type, that is, varchar.

Because the mobile phone number is fixed to 1 1, you can directly use char (11);

However, the bank card number is very long, and they are all numbers. For the convenience of storage, it is uniformly stored as a string type. If the storage type is number, it has exceeded the maximum range of int type, so it is inconvenient to store with bigInteger. Moreover, the numerical value with too many digits will become a scientific counting method, which is not conducive to the normal conversion of data, so it is more convenient to store it with string type.

Char is used to define character variables in C or C++, occupying only one byte, and the range of values is-128 ~+127 (-2 7 ~ 2 7-1). C languages such as int, long, short, etc. When signed or unsigned is not specified, it is signed by default, but char does not specify signed or unsigned in the standard, and the compiler can compile with or without sign.