1, short: decorated int, short integer data, decorated int can be omitted.

2.long: decorated int, long integer data, decorated int can be omitted.

3.long long: decorated int, long integer data, decorated int can be omitted.

4. Signed: modified integer data with signed data type.

5.unsigned: modified integer data, unsigned data type.

6.restrict: used to define and constrain pointers and indicate that pointers are the only and initial way to access data objects.

7.return: used in the function body to return a specific value (if it is void type, the function value is not returned).

8. Continue: End the current cycle and start the next cycle.

9. Break: Jump out of the current cycle or switch structure.

10, goto: unconditional jump statement.

1 1, if: conditional statement without semicolon.

12, else: negative branch of conditional statement (used with if).

13, switch: switch statement (multi-branch statement).

14, branch tag in case:switch statement, used with switch.

15, default: "other" branch in switch statement, optional.

Common functions:

1, int isalpha(int ch) If ch is a letter ('A'-'Z',' a'-'z'), it returns a non-zero value, otherwise it returns 0.

2.int isalnum (int ch) If ch is a letter ('A'-'Z',' a'-'z') or a number ('0'-'9'), it returns a non-zero value, otherwise it returns 0.

3.int ABS (int I) returns the absolute value of integer parameter I.

4.double cabs(struct complex znum) returns the absolute value of complex znum.

5.double fabs(double x) returns the absolute value of double precision parameter X. ..

6.long labs(long n) returns the absolute value of long integer parameter n.

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