C language learning notes (3) -- operators and expressions (I)

 

1 operator and Expression

 

1.1 operator classification:

 

Arithmetic Operator: used for arithmetic operations, including +,-, *, And.

 

Relational operators: used for comparison operations, including>, <, =, and ,! =.

 

Logical operators: used for logical operations, including &, |, and ,! Three.

 

Bitwise operators: bitwise operations by binary, including &, | ,~ And <.

 

Value assignment operator: used for value assignment operations, including =, + =, and & =.

 

Conditional OPERATOR: A three-object operator, used to evaluate conditions (? :).

 

Comma OPERATOR: Used to combine several expressions into one (,).

 

Pointer Operator: Used to get content * and to get address &.

 

Number of nodes OPERATOR: used to calculate the number of bytes occupied by the Data Type sizeof.

 

Special operators: (), [], members (->,.), etc.

 

1.2 Operation Sequence

 

A. Function compute is preferred.

 

B. The second is forced type conversion.

 

C. Auto-increment, auto-subtraction, and inverse.

 

D. multiplication, division, and addition and subtraction.

 

E. Enclose the brackets first.

 

Note: When two consecutive operators appear in an expression, it is best to use spaces to separate them. For example, a ++ B must be written as a ++ B or a ++ B.

 

2. Data Type Conversion

 

2.1 forced type conversion: converts the displayed expression to the required type.

 

Method 1: (type name) (expression ).

 

Method 2: (type name) expression.

 

For example, force type conversion.

 

 

# Include "stdio. h"

# Define PI 3.1415926

Main (){

Int m, n;

Float x, y;

X = 2.5;

Y = 4.8;

M = (int) (x + y);/* convert the floating point type to an integer type */

N = (int) x + m/3;/* forcibly convert x to an integer */

M = n % 4;/* integer remainder */

X = x + y;

Printf ("m = % d, n = % d, x = % f, f = % f", m, n, x, y );

}

Note: Forced type conversion does not change the type attributes of the original variables and expressions, but is only used to convert to the required type.

 

2.2 implicit type conversion: Different numeric types of integer, single-precision, and double-precision types can be mixed for calculation, and implicit type conversion is involved in the operation process.

 

Implicit type conversion rules are: from low to high conversion. For example, char and short can be converted to int.

 

3 Arithmetic Operators and arithmetic expressions

 

3.1 basic arithmetic operators: Include the plus (+), minus (-), minus (*), minus (/), and minus (%) operators.

 

3.2 Special Arithmetic Operators: auto-increment and auto-subtraction.

 

Prefix format: The operation object is first Auto-incremented or auto-subtracted, and then the value of the operation object is referenced as the value of the expression.

 

Suffix format: first reference the value of the computing object as the value of the expression, and then auto-increment or auto-subtraction of the computing object.

 

Example: + + a is equivalent to a = a + 1, -- a is equivalent to a = A-1;

 

A ++ is equivalent to a = a + 1, a -- is equivalent to a = A-1;

 

Note: it can be seen that there is no difference in use alone, but the expressions have different effects.

 

Sample Code:

 

 

# Include "stdio. h"

# Define PI 3.1415926

Main (){

Int I = 6, j = 6, k = 6, h = 6, m, n, x, y;

M = I ++;/* suffix form self-added */

N = ++ j;/* prefix self-increment */

X = k --;/* suffix form auto-subtraction */

Y = -- h;/* suffix form auto-subtraction */

Printf ("\ n I = % d, m = % d, j = % d, n = % d", I, m, j, n );

Printf ("\ n k = % d, x = % d, h = % d, y = % d", k, x, h, y );

}

4. Value assignment operators and value assignment expressions

 

4.1 simple value assignment operator

 

A simple value assignment is used to store the value of an expression to a variable, for example, a = 4;

 

Note: The left side of the value assignment operation must be a variable;

 

The priority of the value assignment operation is relatively low ,;

 

4.2 compound assignment operator

 

Is to combine the operation and value assignment, such as + =,-=, and so on.

 

For example, m + = 3 is equivalent to m = m + 3;

 

4.3 assignment expression operation

 

Note the following when using expressions:

 

4.3.1 composite value assignment operator.

 

Sample Code:

 

 

# Include "stdio. h"

# Define PI 3.1415926

Main (){

Int x = 2, y, z;

X * = 3 + 2;/* is equivalent to x = x * (3 + 2 )*/

Printf ("(1) x = % d \ n", x );

X * = y = z = 4;/* is equivalent to y = z = 4, x = x * y */

Printf ("(2) x = % d \ n", x );

X = y = 1;

Z = x +-1;/* equivalent to y = X-1, x = X-1 */

Printf ("(3) x = % d *** z = % d \ n", x, z );

Z = x ++ * ++ y;/* is equivalent to y = y + 1, z = x * y, x = x + 1 */

Printf ("(4) x = % d *** y = % d *** z = % d \ n", x, y, z );

}

4.3.2 value assignment conversion: If the types on both sides of the operator are different but both are numerical values or characters, C will automatically convert the corresponding types.

 

Sample Code:

 

 

# Include "stdio. h"

# Define PI 3.1415926

Main (){

Int a, B = 322;

Float x, y = 8.88;

Char c1 = 'k', c2;

A = y;

X = B;

A = c1;

C2 = B;

Printf ("% d, % f, % d, % c", a, x, a, c2 );

}

 

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