C language - control statement

C Language is a structured language , also C Language is to solve things in life .
Control statement is the execution flow of control program , Implement various structural ways of the program .
Programs are used to solve problems in life , A program is made up of various statements , Control statements are used to control the execution flow of a program , Implement various structural ways of the program . Control statements are auxiliary statements , The program needs to realize the problems in life , So the program needs to realize these structural ways in life , So the control statement helps the program Realization These structural modes , So it's called Control statement .

Everything in our life can be abstracted into one of three structures , Or some combination of these .
With these three structures, we can describe things in our life .
C Language is for writing programs , The program is written to solve things in our life , Let things in life be solved by computers , So at this point C Language must be able to describe these structures , To provide our program , therefore C Language produces control statements , This is it. C The power of language , Be able to describe these structures .
C Language can describe these structures , So say ,C Language is a structured programming language .
Program - solve , Realize things in life
Things in life can be abstract , Split 1 In three structural ways （ The order , choice , loop ）
The procedure is made by C Write in language .
therefore C Language should provide these abilities , Be able to describe these structures in life .
Use this way C The program written in language can describe all kinds of things in life .
Program is to describe things in life , When something in life needs to be done repeatedly , But when doing it repeatedly , I find that I don't need to do it repeatedly , The result has been obtained , So in order for the program to realize such functions ,C Language provides break sentence ,break Statement can make the program end the loop , When will the cycle end , You need control statements to control break sentence , Choose here if -else sentence . When something in life is being done repeatedly , At a certain repetition , Don't want to do the next thing , Want to skip the next thing , Doing it again , For example, a person has to eat every day , rest , This is a repetitive thing , But every Friday , Don't want to rest , So skip the rest , Wait for Friday , Just keep repeating it .
getchar
That is, you are constantly learning in life , Keep learning this thing over and over , But in the process of learning , Met a rich woman , Then the repetition of learning will be stopped , I won't study anymore , That is to stop the cycle .
That's because the program is to realize things in life , So the program must also be able to implement this way , therefore C Language provides break sentence , When in a loop , If a certain condition is reached , Then use break sentence , It will end the cycle , Like in life , If there is a rich woman , Will stop learning , Reached a certain condition .
break Application scenarios of , If a certain condition is reached, the cycle will be terminated
If a rich woman appears in life , Will stop learning , Rich woman is that condition .
continue Application scenarios of , If a certain condition is reached , Just skip the statement after this loop , Go straight to the next cycle .
For example, you are playing the game of clearance , If you are in the second level , dead , Are you unable to perform the remaining tasks in the second level , Return to the second level , Come back .
Death is the condition , When a certain condition is reached , Just skip the loop .
Because the program is to realize things in life , So the program should be able to implement this way , therefore C Language provides programs with continue sentence , When executed continue sentence , Will skip this cycle , To the next cycle .

and break and continue sentence , It can be executed , It can also be done without , To control execution , You need to use control statements
And when you meet a rich woman in life, you will stop learning , If you don't meet a rich woman, you will continue to study
That program in order to achieve such a way , How does it control to stop learning and continue learning ？
Use control statements to control execution , Then stop learning , How should this be achieved ？
C Language developed break sentence , You can stop , therefore C Language uses control statements to control break Statements, etc .

getchar Functions and scanf Function reads data in the input buffer , When there is no data in the input buffer , Will wait for input , After typing data on the keyboard , Press enter and the data will be compared with \n, Put in the input buffer ,getchar Function can only read one character at a time ,scanf Function can read multiple characters , When a space is encountered , Will stop , Or no space , Read \0 Previous data .
getchar() The function reads a character into the input buffer , Characters to be read , Return character's ascii value ,ascii Value is number , So the number returned , Put it in int Type variables , Instead of char Variable of type , because char The space of a variable of type is only one byte , And the type of number is int Type , It takes four bytes , So you have to use int Type of variable to receive .
And after input error or reading , Will return a EOF, and EOF yes -1, It's also numbers , So we must use int Type of variable to receive .
So how to make getchar Stop ？
Press on the keyboard ctrl+z,getchar After reading the characters we entered , It will return EOF
After pressing other data on the keyboard ,getchar After reading our characters , Characters will be returned ascii value .
When you return , because ascii Values and EOF It's all integers , So use integer variables to receive , Instead of using character variables to receive , Because you want to receive integers instead of characters .
putchar Is the output function

The principle of keyboard input ：
When we press the key on the keyboard , Press enter after , It will put the corresponding letter of the key we pressed into the input buffer , If you don't press enter , It will not be put into the input buffer , The character corresponding to the Enter key is \n, So after input , The input buffer will have a string of characters + The Enter key corresponds to \n.
scanf The function is where the data is read , Not read directly from the keyboard , Instead, read in the input buffer , And can't read \n, But when encountering a space character, it will stop , Only read before or \n Previous characters , Picky eaters .
getchar Where the function reads data , Also read in the input buffer , It can only read one character at a time , And not picky about food , encounter \n, It can also read .
So when we use scanf After the function reads the data , The input buffer will leave a \n, If there's something in the back getchar function , Will read directly \n.
But if we don't want getchar read \n. Want him to read other values , So use an extra getchar function , Let him read it first \n, At this point, the input buffer is clean , nothing in the world ,getchar Waiting for input , We type on the keyboard , Push the input character into the input buffer ,getchar In the reading .
As long as there are characters in the input buffer , No matter what character it is ,getchar Metropolis Read To , The characters that will be entered into the buffer take come out , then getchar Function after reading , It will return characters ascii value .
If there are other characters in the input buffer , But we don't want this getchar Read , So let these characters be used by the rest getchar Read , After reading , It's our turn getchar. Then the rest getchar When will you finish reading ？ If getchar After reading , The value returned is EOF, If it is EOF Will stop reading , Will jump out of the reading cycle ,

C How does a language stop a loop , Use break. So how to control the stop cycle ？ Use control statements to control , Then how to stop the cycle ? Use break sentence , So use control statements to control break sentence .
You can cycle or not cycle , that C How language controls circulation and non circulation ？ Use control statements , If you meet the conditions, cycle , Stop the cycle if the conditions are not met , So you can use ifelse sentence .
that C How does language achieve non cyclic ？ Use break sentence , You can stop the cycle .

Everything in life can be abstracted into three structural ways （ The order , choice , loop ）
C Program written in language , To realize the problems in life , Solve problems in life .
That program in order to achieve this structure , So there are control statements , It is an auxiliary statement , Help the program realize these structural ways .
There are many choices in life , Add bits , You can mess it up , You can study hard , You can also exit .
therefore C Language provides choice statements , Realize these options , This is one of the control statements , By controlling other statements to achieve several structural ways .
When implementing the selection structure , Use ifelse Statement to control other statements to implement the selection structure , When conditions are met , Just execute some statements , When the conditions are not met , Do not execute certain statements , The selection structure is realized .
You need to keep learning in life , This is a repeated process . It's a circular structure
The program needs to implement this structure , A circular statement appears , If the conditional expression is satisfied , It's going to keep cycling , Until not satisfied , Stop the cycle , Go through the loop statement control Other statements implement loop structures .
How do loop statements, as control statements, control other statements ？ If the conditional expression is satisfied 1 Will cycle , If you are not satisfied, you will not cycle .
When learning repeatedly , Met a rich woman , Here comes the choice , Program usage if-else The control statement implements this selection structure , When conditions are met , Just execute some statements , If you don't meet the conditions, you won't execute .
After meeting a rich woman , There's no need to learn , Just jump out of the repetitive process of learning , There is no need to repeat , End this cycle .
In order to realize the way that the program can jump out of the loop , Use break Statement can realize this way .
When playing games in customs clearance , Reached the second level , You were killed , We need to play the second level again , Skip the level after the second level , Restart the second level .
In order to realize this way , Use continue This can be achieved .

When entering data on the keyboard , Finally, press enter , This data will be sent to the input buffer , The character corresponding to the Enter key is also sent to the buffer .
scanf The function reads data in the input buffer , It is picky about food , Space encountered , perhaps \n, Will not read data
getchar The function also reads data in the input buffer , It is not picky about food , Any character , He can read , But call once , Only one character can be read .
Read means to take away the characters in the input buffer , It's not a copy .
gets Functions are also read functions , It makes up for scanf The disadvantages of functions ： Picky food , It can read spaces , But I can't read \n.
They are all functions , Just call them , Will execute ,getchar Only one data can be read at a time ,scanf Function can read single data , You can also read a string of characters .getchar Poor ability , Read only one ,scanf You can choose to read one , You can also read several .
getchar Function after reading characters , What is returned is the character of ascii value , And reading errors , Or after reading , The return is EOF,EOF Namely -1, So all the returned values are integers , To be stored in an integer variable , If the returned value is character , Then put it into a character variable .

Everything in life can be abstracted as a choice structure , Sequential structure , Loop structure
So everything in life can be abstracted as one of them , Or a combination of several .

The program chooses the structure in order to realize ,C Language provides ifelse sentence , adopt if and else Conditional expression in , Satisfy expression , execute , Not satisfied, not executed , Constitute a selection structure , So as to realize the selection structure .
In order to realize the loop structure ,C Language provides for,while,do-while sentence , So as to realize the circular structure

Some things in life need to be done repeatedly , Form a circular structure , Use loop statements to achieve , Use circular statements to control Repeat other statements , Implement loop structure , Satisfy the cyclic condition , Just cycle , It doesn't satisfy the cyclic condition , Just exit the loop

When you choose not to do it again , It forms the selection structure , Need to use if-else Statement to implement the selection structure .
Don't repeat , To exit the loop , In order to exit the loop ,C Language provides break sentence , By using ifelse Statement to control break sentence .