Initialization of ' XXX ' is skipped by ' case ' label causes and solutions

Today, after reading the information on the Internet, I found the reason, namely:

You cannot define a variable in a switch case, or you will get an error. It is possible that the initialization of a variable is skipped because sometimes the case condition is not executed.

Then think of three solutions:

1: Replace the switch statement with if else;

2: Enclose the code in case {} so that the variable can be defined in {};

3: If the variable is used in each case, define the variable outside of switch;

Initialization of ' XXX ' is skipped by ' case ' label causes and solutions