Branch and loop statements

1. There are nine kinds of control statements .

It can be divided into three categories ：

• Conditional judgment statements are also called branch statements ：if sentence 、switch sentence ;
• Loop statement ：do while sentence 、while sentence 、for sentence ;
• Turn to statement ：break sentence 、goto sentence 、continue sentence 、return sentence .

1. Select statement （ Judgment statement ）

if sentence

• Format ：if（ expression ）

sentence 1;

else

sentence 2;

When the value of the expression is non 0 When （ It's true ）, Execute statement 1, Otherwise, the result is 0（ For false ）, perform else The sentence of 2.

• Under normal circumstances, the statement 1 And statement 2 There is not only one statement , Instead, there are multiple statements .

Multiple use curly brackets （{}） Cover up , As a statement 1 Or words 2;

• Be careful ;else Always with the nearest one and not with others else Paired if sentence

for example ：

The following is the correct matching method

• Don't confuse == and =

==（ Double equal sign ） It's about judging whether it's equal ,= It's assignment

• Conditional expression

Format ： expression 1？ expression 2: expression 3

It represents if expression 1 It's true , Execute expression 2, For false , Execute expression 3.

switch sentence

• Format ：

switch( Integer expression )

{

  case Integer constant expression :

   sentence ;

}

• Under normal circumstances , We can't use to complete the real Branch , So we use break load case Statement to implement the real Branch ;

We can also put a few case Close , Share one statement , To save code

• If the expressed value is the same as all case What if the values of the tags don't match ？

When switch The value of the expression does not match all case The value of the tag , This default The statement following the clause will execute .

therefore , Every switch Only one... Can appear in the statement default Clause .

But it can appear anywhere in the statement list , And the statement flow will execute a case Execute as tag default Clause .

1. Loop statement

while sentence

• Format ：

while( expression )

Loop statement ;

• continue stay while The role of the loop is ：

continue Is used to terminate the cycle , In this cycle continue The following code is no longer executed ,

It's a jump to while The judgment part of a sentence . Make the entry judgment of the next cycle .

• example ： Dichotomy search

for sentence

• for( expression 1; expression 2; expression 3)

Loop statement ;

expression 1

expression 1 For the initialization part , Used to initialize loop variables .

expression 2

expression 2 For the conditional judgment part , Used to determine when a loop ends .

expression 3

expression 3 For the adjustment part , For adjustment of cyclic conditions

• example ：

#include

int main()

{

char arr1[] = "welcome to bit...";

char arr2[] = "#################";

int left = 0;

int right = strlen(arr1)-1;

printf("%s\n", arr2);

for (left=0, right=strlen(src)-1;

  left

  left++, right--)

 {

  Sleep(1000); This is window Function parameters under , In milliseconds .

  arr2[left] = arr1[left];

arr2[right] = arr1[right];

    printf( "%s\n", target);

 }

retutn 0;

}

do while sentence

• do

Loop statement ;

while( expression );

Circular statements , If there is not only one , It needs to be enclosed in curly brackets

• i++ stay continue Behind , Lead to an endless cycle .

break and continue sentence

• break The statement is to jump out of this cycle .
• continue The statement is to skip this loop , The next few times continue , But it is prone to dead circulation , There will be different results , If you pay attention to continue The positional relationship between statements and loop statements .

Guess the number game to achieve （ Half search algorithm ）

example ：

rand Is a function that generates random values , The header file is #include .time（null） It's a function of time , The header file is time.h,time You need to put a pointer in the parentheses of the function , utilize null Null pointer , Come on

Form a constantly changing timestamp , To keep changing the value of random values .rand You also need to quote a srand function .