C language learning notes (iv) -- operators and expressions (II)

 

1. Comma operator and comma expression

 

1.1 comma expression format: expression 1, expression 2, expression 3,..., expression n;

 

This expression is used to calculate expression 1, expression 2, expression n, and the value of the last expression.

 

1.2 priority of a comma expression: lowest.

 

1.3 values of the comma expression:

 

Sample Code:

 

 

# Include "stdio. h"

Main (){

Int a, B, c;

A = 1, B = 2, c = a + B + 3;

Printf ("% d, % d, % d \ n", a, B, c );

C = (a ++, a ++ = B, a-B);/* variable c saves the value of the comma expression */

Printf ("% d, % d, % d \ n", a, B, c);/* the comma expression is used to evaluate the Order */

}

The output result is as follows:

 

1, 2, 6

 

4, 2, 2

 

2. Relational operators and expressions

 

True and false values in 2.1C: C language does not contain Logical Data. Therefore, the C language specifies that the true value is expressed by an integer constant 1. All non-0 expressions and the logical values of constants are 1, the integer constant 0 indicates the dummy value. Only constants whose expression value is 0 and the logical value of the expression are 0.

 

Link expression example code:

 

 

# Include "stdio. h"

Main (){

Char x = 'M', y = 'n ';

Int n;

N = x <y;/* obtain the value of the relational expression x <y */

Printf ("% d \ n", n );

N = x = Y-1;/* Get the relational expression x = the value of the Y-1 */

Printf ("% d \ n", n );

N = ('y '! = 'Y') + (5 <3) + (Y-x = 1);/* Get the value of the relational expression x = Y-1 */

Printf ("% d \ n", n );

}

 

Program running result:

 

1

 

1

 

2

 

Relational expressions participate in arithmetic operations:

 

 

# Include "stdio. h"

Main (){

Int a, B, c;

A = B = c = 10;/* variable a, B, c assigned initial values */

A = B = c;

Printf ("a = % d, B = % d, c = % d \ n", a, B, c);/* pay attention to the difference between equal signs and value assignment numbers */

A = (B + (c ++> 2 ));

Printf ("a = % d, B = % d, c = % d \ n", a, B, c );

/* The relational expression value can be set in the c ++> 2 operation. values 1 and B are added to a for storage */

A = B> c * 100;

Printf ("a = % d, B = % d, c = % d \ n", a, B, c );

/* Pay attention to the priority of calculation when using relational expressions */

}

Program running result:

 

A = 1, B = 10, c = 10

 

A = 11, B = 10, c = 11

 

A = 0, B = 10, c = 11

 

3 logical operators and logical expressions

 

3.1 basic logical operators include: single object operators !, Binary operators &, |.

 

Example code of logic and operator:

 

 

# Include "stdio. h"

# Define PI 3.1415926

Main (){

Int m, n;

Int k;

K = (m = 0) & (m = 1 );

Printf ("% d, % d \ n", m, k );

K = (m = 1) & (m = 0 );

Printf ("% d, % d \ n", m, k );

K = (m = 2) & (m = 1) & (m = 0);/* test multi-layer logic and Operation Rules */

Printf ("% d, % d \ n", m, k );

M = 0, k = 0;

N = k ++ & m ++;

Printf ("% d, % d, % d \ n", k, m, n );

M = 0, k = 0;

N = m ++ & k ++;/* test expression k ++ & m ++ and m ++ & k ++ */

Printf ("% d, % d, % d \ n", k, m, n );

}

Program running result:

 

0, 0

 

0, 0

 

0, 0

 

1, 0, 0

 

0, 1, 0

 

Example code of logic or operator:

 

 

# Include "stdio. h"

Main (){

Int m, n;

Int k;

K = (m = 0) | (m = 1);/* Calculation rule of logical or operation */

Printf ("% d, % d \ n", m, k );

K = (m = 1) | (m = 0 );

Printf ("% d, % d \ n", m, k );

K = (m = 2) | (m = 1) | (m = 0);/* multi-layer logic or operation rule test */

Printf ("% d, % d \ n", m, k );

M = 0, k = 0;

N = ++ m | ++ k;

Printf ("% d, % d, % d \ n", k, m, n );

M = 0, k = 0;

N = ++ k | ++ m;

Printf ("% d, % d, % d \ n", k, m, n ); /* test expression ++ k | ++ m and ++ m | ++ k ++ */

}

Program running result:

 

1, 1

 

1, 1

 

2, 1

 

0, 1, 1

 

1, 0, 1

 

Example code of logical and logical or hybrid operations:

 

 

# Include "stdio. h"

Main (){

Int m, k;

K = (m = 0) | (m = 1) & (m = 2);/* expression interpreted as (m = 0) | (m = 1) & (m = 2 ))*/

Printf ("% d, % d \ n", m, k );

K = (m = 2) | (m = 1) & (m = 0);/* expression interpreted as (m = 2) | (m = 1) & (m = 0 ))*/

Printf ("% d, % d \ n", m, k );

K = (m = 2) & (m = 1) | (m = 0);/* The expression is interpreted as (m = 2) & (m = 1) | (m = 0 )*/

Printf ("% d, % d \ n", m, k );

K = (m = 0) & (m = 1) | (m = 2);/* The expression is interpreted as (m = 0) & (m = 1) | (m = 2 )*/

Printf ("% d, % d \ n", m, k );

}

Program running result:

 

2, 1

 

2, 1

 

1, 1

 

2, 1

 

4. Conditional operators and conditional expressions

 

4.1 condition operator "? : "Is the only three-object operator in C language. It has a higher priority than the value assignment operation.

 

Expression syntax: expression 1? Expression 2: expression 3

 

The execution order is: first solve expression 1. If it is 0, execute expression 2; otherwise, execute expression 3.

 

Sample Code:

 

 

# Include "stdio. h"

Main (){

Char ch;

Scanf ("% c", & ch);/* enter a character and assign it to the variable ch */

Ch = (ch> = 'A' & ch <= 'Z ')? (Ch + 'a'-'A'): ch;/* If the character is an upper-case letter, convert it to a lower-case letter */

Printf ("\ n % c", ch );

}

5sizeof Operator

 

5.1sizeof is a single-object operator in C language. The calculation object is a variable name, expression, or data type identifier. The function provides the storage size of the operands in bytes.

 

5.2 syntax format: sizeof (expression) or sizeof expression or sizeof (data type)

 

6. Obtain the address Operator

 

6.1 The calculation object of the address operator can only be a variable, and the calculation result is the storage address of the variable.

 

7 mixed operation

 

Sample Code:

 

 

# Include "stdio. h"

Main (){

Int x, y = 1, z;

X = (9 + 6) % 5 >=9% 5 + 6% 5 )? 1:0;/* (9 + 6) % 5> = 9% 5 + 6% 5) is equivalent to (9 + 6) % 5)> = (9% 5 + 6% 5) the value is 0 */

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

Y + = z = x + 3;/* y + = z = x + 3 Equivalent z = x + 3, y = y + z */

Printf ("y = % d \ t z = % d \ n", y, z );

X = y = z = 1;

-- X & ++ y | z ++;/* Mixed logic and logic or operation */

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

}

Program running result:

 

X = 0

 

Y = 4 z = 3

 

X = 0 y = 1 z = 2

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