MOOC Weng Kai C language fourth week: further judgment and circulation: 1. Logical types and operations 2. Judgment of cascading and nesting

One . Logical types and operations

1. Logical operations ： Logical operation is the operation of logical quantity , It turns out that 0 or 1.

The result of a system operation or logical operation .

  Logical operations are performed from left to right .

Don't assign values to , Including compound assignments combined into expressions .  

2. Conditional operator

count=(count>20)?count-10:count+10;

?  The one in front is Conditions

?  The back is Value after conditions are met

 :  The back is   The value after the condition is not satisfied

_ amount to

if(count>20)

  count=count-10;

else

  count=count+10;( Something left over from the early days of programming languages )

3. The comma operator

Commas are used to connect two expressions , and Take the value of the expression on its right as the result of its operation .

eg:   i=(3+4,5+6)   The result is 11, namely  i=(3+4,5+6)

The priority of commas is the lowest of all operators , So the expressions on both sides of it will be evaluated first ; The combination of commas is from left to right , So the expression on the left will evaluate , The value of the expression on the right is left as the result of the comma operation .

eg:i=3+4,5+6  The result is 7, namely i=3+4,5+6 

Comma expression is mainly in for Use of （ At present, there is only one use ）： When you want to be in for When placing multiple calculations ：

for(i=0,j=10;i<j;i++,j--)

Two . Cascading and nested judgments

1. Nested if-else

else Always the nearest one if matching , Indent format cannot imply if else The matching of .

Suggest ： stay if or else Always use... In the back {}, Even when there is only one sentence .

2. Cascade if-else

if(exp1)

   st1;

else if(exp2)

   st2;

else 

   st3;