Rules for comma expressions and self-increment decrement operators and type conversions

Comma operator

The comma operator has the lowest precedence;

The comma operator is used to split multiple expressions;

The result of a comma-expression consisting of a comma operator is that the result of the last expression

Attention:

int i;

i = 3,4,5,;

The value of I obtained from the above statement is 3

i = (3, 4, 5);

The resulting value of I is 5

Summarize:

++i Pre-increment: First add 1 to the value of I and then use the value of 1 to participate in all subsequent operations

i++ lag self-increment: First use the original value of the variable to participate in all subsequent operations, until all operations of this statement are completed, the value of the variable is added minus 1

Lag self-increment in the table of special performance: First use the original value to participate in the condition of judgment, and then immediately from increase or decrease;

The special behavior of the lag self-increment in the comma expression:

int i = 3, j = 4, K;

K = (++i, j + +, i++ * ++j);

printf ("%d%d%d\n", I, J, K);

Results:

i = 5;

j = 6

K = 24

Summarize:

Hysteresis increment occurs immediately when a comma operator is encountered, except for a parameter comma in a function

Data type conversions

1.1) Automatic type conversion

In one operation, if the data types of the two operands participating in the operation are inconsistent, the C language will convert the data type to its own custom and follow the following guidelines:

The short-integer is closer to the long integer type;

Simple data types move closer to complex data types;

Here are two examples:

5.0 + 1/2

=5.0 +0

=5.0+0.0=5.0

5+1/2.0=5+1.0/2.0=5+0.5=5.0+0.5=5.5

Mathematical formula: 1/1+1/2+1/3+.....+1/n

int i;

Double s = 0;

for (i = 1; I <= n; i++)

s + = 1.0/i;

1.2. Forcing type conversions

Grammar:

(data type conversion) expression

s + = (double) 1/i;//forced type conversion is also an operator, which is the lowest of the monocular operator

Coercion of type conversion with human will as principle

s + = (double) (1/i);//Just get 0.0

Forcing a type conversion operation is absolutely impossible to change the data type of a variable

1.3 Automatic coercion of type conversions

This operation only occurs in assignment operations.

char C = 97.14159;

Some precision will be lost at the time of assignment, the output lowercase a

Double f = ' A ';

Output 65.000

Conversion principle: If the data types on both sides of the assignment operator are inconsistent, the value of the right expression of the assignment operator is automatically converted by the C language, and is based on the left value data type on the left side of the assignment operator;

Rules for comma expressions and self-increment decrement operators and type conversions