1. Identifier , case sensitive
First character: a~z, A~Z, _ , @ are allowed, numbers are not allowed
Other characters: a~z, A~Z, 0~9, _ are allowed, @ is not allowed
@ can be placed in the first place, but is not recommended as a common character
2. Naming Conventions
Pascal case: used for type names and member names, with the first letter of each word in the identifier capitalized
Camel case: For local variables and method parameters, all words in an identifier except the first are capitalized
All caps: for abbreviations only
3. Keywords
Keywords cannot be used as variable names or other forms of identifiers unless they start with the @ character. All C# keywords consist of all lowercase letters, but .NET type names use the Pascal case convention
4. Format String
Console.WriteLine(“Two sample integers are{0} and {1}”,3,6);
{0} and {1} are surrogate tokens, 3 and 6 are surrogate values
The output is Two sample integers are 3 and 6
Console.WriteLine(“Three sample integersare {1}，{0} and {1}”,3,6);
The output is Three sample integers are 6,3 and 6
Console.WriteLine(“Two sample integers are{2} and {1}”,3,6);
Running error, because there is no position 2 in the code, 3 is position 0, 6 is position 1