C Language Foundation---constants, operators, functions

C Language Foundation---constants, operators, functions

One, variable

1. Name rules for variable names

1) The first character must be a letter or an underscore, followed by a letter, a number, or an underscore. The following are lawful:

Sum, _total, li_ling

Illegal: zhang-sum, 136, student ' s

2) uppercase and lowercase letters represent different characters

3) The length is not infinite

4) try to be concise and easy to remember, see the name of the idea

5) Different variables cannot take the same variable name in the same function

2. Variables must be "defined first, then used"

3, at the time of compiling, must pay attention to the validity of variable operation. For example, integer variables can be redundant, if A and B are defined as Integer variables, you can perform a%b operations to find the whole remainder of a by B, and if it is a real variable, it is not allowed to do the redundancy operation

4. Integer variables:

Basic integer: int

Length int: Long int.

Short integer: Shorter int

int is signed by default, unsigned at the front plus unsigned

5, the Real type variable

Single precision: float

Double precision: Double

Long double-precision: Long Doubles

The output is no longer "%d", it becomes "%f", "%1f,%2f" is reserved one, or two decimal places

6, Character type variable

Character type name: Char

Characters are enclosed in a single apostrophe, and a character variable is output with an alphabetic character:%c

7. Escape character

/n	Line break
/t	To jump the next output data to the next output area
/b	Backspace
/R	Enter
/F	Page change
/0	Empty operation
/ddd	Characters represented by 1-3-bit octal
/xhh	Characters represented by 1-2-bit hexadecimal

Convert lowercase letters to uppercase

Program:/* Lowercase converted to uppercase letters */

#include "stdio.h"

void Main ()

{

Char c1= ' A ', c2= ' B ';

c1=c1-32;

c2=c2-32;

printf ("%c,%c\n", C1,C2);

}

Result is a, b

The lowercase letter of the ASCLL code currency is large 32, so subtract 32

8. String constants

A string constant is a sequence of characters enclosed in double apostrophes: ""

C= "KADFJ";

This is a bad syntax because a string constant cannot be assigned to a character variable and must be stored in a character array

Second, operator

1 , Arithmetic

+	Addition operation
-	Subtraction operations
*	Multiplication operations
/	Division operation
%	To find the remainder operation
i++,i--	Let I plus minus before using I
++i,--I	I plus minus after I use I
+	string addition

Note: The sequence of operations is the same as the number operation, from left to right in the same level

When a modulo operation is performed, if there are negative numbers, the result of the operation depends on whether there are negative numbers on the left

String data and any data using + are connected and eventually become strings.

Self-increment, the self-subtraction operation applies only to variables

2. Relational operators

>	Greater than
<	Less than
==	Equivalent to	different from =
>=	Greater than or equal
<=	Less than or equal
!=	Not equal to

3. Logical operators

！	Non -
&&	And
||	Or

4 Assignment Operator: =

and "= =" must be differentiated, "=" is only the assignment, and "= =" is about equal to

Priority level	Operator	Meaning	Number of operand objects required	Combination method
1	( ) [ ] → ·	Parentheses Subscript Operation Index Pointer to struct member operator struct Member operators		From left to right
	!"    ~    ++    --    -   (type)    *    &   sizeof	Logical non-operator Bitwise negation operator Self-increment operator Decrement operator Minus sign operator Type conversion operator Pointer operator Address and operator Length operator	1      (monocular operator)	",       From right to left
3	* / %	Multiplication operator Division operator Remainder operator	2 (Binocular operator)	From left to right
4	+ -	Addition operator Subtraction operator	2 (Binocular operator)	From left to right
5	<< >>	Left shift operator Right shift operator	2 (Binocular operator)	From left to right
6	<<=︺>>=	Relational operators	2 (Binocular operator)	From left to right
7	= = ! =	equals operator Not equal to operator	2 (Binocular operator)	From left to right
8	&	Bitwise-AND operator	2 (Binocular operator)	From left to right
9	^	Bitwise XOR OR operator	2 (Binocular operator)	From left to right
10	︱	Bitwise OR operator	2 (Binocular operator)	From left to right
11	&&	Logic and operators	2 (Binocular operator)	From left to right
12	‖	logical operators	2 (Binocular operator)	From left to right
13	?：	Conditional operators	2 (Binocular operator)	From left to right
14	=+=-=*= /=%=>>=<<= &=^=︱=	Assignment operators	2	From right to left
15	，	Comma operator (sequential job search operator)		From left to right

Description

(1) Operators of the same precedence have the same precedence, and the order of operations is determined by the binding direction. For example, * and/have the same priority level, its binding direction is from left to right, therefore, the 3*5/4 order of operations is first multiply after the divide. One and + + are the same priority, and the combination direction is from right to left, so-i++ is equivalent to one (i++).

(2) Different operators require different operands, such as 10 (plus) and-(minus) as binocular operators, requiring an operand (such as 3+5, 8-3, and so on) on either side of the operator. The + + and-(minus) operators are unary operators that can only appear on one side of the operator (such as-A, i++ 、--I, (float) I, sizeof (int), *p, and so on). The conditional operator is the only three-mesh operator in C, such as X?A:B.

(3) The precedence of various operators can be summed up from the above table:

Elementary operator () []→

↓

Monocular operator

↓

Calculating operator (first multiplication, then plus minus)

↓

Relational operators

↓

logical operators (not included!)

↓

Conditional operators

↓

Assignment operators

↓

Comma operator

The priority levels above are decremented from top to bottom. The primary operator has the highest precedence and the comma operator has the lowest precedence. Bitwise operators are more decentralized in their precedence. For easy memory, you can add an arc number when using the bitwise operator.

C Language Foundation---constants, operators, functions