The third level of C language punch in

One 、 Cast expression

form :（ Type name ） expression

function ： Converts the value of an expression to the specified data type

（double） 1/2 The value of is 0.5      （ As mentioned in the last section 1/2 It's two integers Should the 0 Because there is a double, The value is decimal 0.5, amount to （double）1/2 Equivalent to 1.0/2）

The level of cast takes precedence over division

  This table describes the transformation rules more vividly

Two 、 Assignment expression

form ： Variable name = expression

On the left is a variable name , Get the value of an expression on the right , Assign the value of the expression to a variable , Its combination is

From right to left , Its priority is only higher than comma operator . The value of the assignment expression is the new value obtained by the leftmost variable .

Simply put, it's the left A variable , On the right is an equation . such as ：a=2+7/3

(1) Compound assignment expression

such as   n+=1 Equivalent to n=n+1

n*=m+3 Equivalent to n=n*(m+3)

Yes : =  += -= /= %=  &= ^= wait     associativity ： From right to left

(2) Type conversion in assignment operation

int x;
x=6.5;     //x Integers 6, Here is a transformation , Convert to be consistent with the type of variable 
double y;
y=6;       //y by 6.0, Here is a transformation , Convert to be consistent with the type of variable 

3、 ... and 、 Auto increment and auto decrement operator

Self adding 、 The subtraction operator is ++ and --. Self adding ( reduce ) Operator in front , First increase ( reduce ） After use ; Self adding ( reduce ) Operator after , Use first and then increase ( reduce ). The combination direction of operators is from right to left ,-k++ Equivalent to -（k--）.

Self adding ( reduce ) There are often two operations in the operation ： Calculate the value of the expression and the value of the variable .

set up k=3, Calculate the value of the following assignment expression and calculate the value of the variable

expression	x Value	k Value	The value of the assignment expression
x=k++	3	4	3
x=++k	4	4	4
x=k--	3	2	3
x=--k	2	2	2

As can be seen from the table :++ Must make k increase 1,-- Must make k reduce 1, Because it is an assignment expression , therefore x The value of is interlinked with the value of the expression

Four 、 Comma operators and comma expressions

form : expression 1, expression 2,....., expression n

Combination direction : From left to right

Operational rules ： So let's evaluate the expression 1 Value , And then evaluate the expression 2 Value , And then calculate the expression 3 Value ,..... Finally, calculate the expression n Value , expression n The value of is the value of the entire comma expression

The comma expression has the lowest priority , Lower than assignment

int x=8,y=12,z=14
x++,y=z++,z=++x;
y=x%z--;
//  Last x=10 y=0,z=9

answer :

The original x=8 You can see that from the top Yes x++ Add a ,++x Once again, , Total increase 2 Time , Namely 8+2=10

The original y=12 y=X%z--  here x=10 z=10 because z=++x ,z-- Is the suffix with the previous value 10 To participate in the calculation , therefore 10%10=0 ,y Is equal to 0

The original z=14 First, y=z++ ,z=15 also z=++x ,z be equal to 10, Last z-- Say with z=9

Answer of last issue :

#include<stdio.h>
void main()
{
      double a,b,c;  // Define three real numbers 
      double sum,aver;  //sum Storage and ,aver Store the average 
      scanf("%lf%lf%lf",&a,&b,&c);  // Input 3 A real number 
      sum=a+b+c;        // Calculation 3 Sum of numbers 
      aver=(a+b+c)/3;  // Calculation 3 The average of the numbers 
      getchar();
      getchar();
}

This assignment

1. Enter the of the triangle 3 Strip side length , Find the area of three triangles （ Query the formula on the Internet , I will use the square function sqrt, File header is required math.h）

2. Input 2 Number , In exchange for 2 The value of the number

for example : x=2 ,y=3 After exchanging x=3,y=2