Integer constants have decimal, octal (starting from 0) and hexadecimal forms (starting from 0x).

End with l, end with u, and end with LL means long int, unsigned, long long int (i64).

Different types of data have their own data ranges.

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There are other types of constants in C language, such as character constants:' a',' b','%' and so on. , enumerated literal constants, Boolean literal constants, etc. Their values are essentially integer constants.