[C language - zero foundation lesson 6] input and output sentence format and compound sentence

Preface

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This issue is about C Language input and output statement related formats and compound statements , If there is any mistake, you are welcome to put forward your views .

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Catalog

What is assignment 、 What is an assignment statement ？

Data input statement

example 1： String output as is

example 2. Specify width output

Data input

example 1： String output as is

example 2. Specify width output

example 4： Real data input

Character input and output

Number and character assignment

Character input function ：getchar

Character output function ：putchar

Compound statements and empty statements

Empty statement

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What is assignment 、 What is an assignment statement ？

In life, when we pour water into the cup, it is assignment , A cup is a container for storing things . stay C In language, variables are equivalent to a container used to store values , Different types of variables store different things . for example ： The cup is filled with water 、 The picture frame is for photos 、 The clip of a pistol is used for loading bullets , Different things are packed in different containers .

C Used in language = To represent the assignment . Two equal signs == stay C Language means judgment .

for example ：

int a=10

C Language a set of statements must end with ; 

Composition of assignment statement ： Add ; Is the assignment statement .

for example ：

int a=10;

C In language ; The expression is a statement .

Data input statement

printf(“ character Format specification Escape character ”, Output item );

example 1： String output as is

 int x = 123;
	float y = 12.12;
	printf("x=%d,y=%f\n",x,y);
	printf("%d,%f", x, y);

result ：

x=123,y=12.120000
123,12.120000
 

example 2. Specify width output

 int x = 123;
	printf("x=%4d\n",x);
	printf("x=%2d\n",x);

result ：

x=123
x=123
Be careful ： first line x=123 There is a space here .

summary ： If you specify the length > Fill in blank space for actual length , Positive numbers ： Front edge patch , negative ： Back filling .

 float t=23.12345678;
	printf("f=%7.2f\n",t);
   printf("f=%10.6f\n",t);

  result ：

f=  23.12        Two spaces
f=23.123457 A space
%n.mf：m Represents the total length of data ,n For decimal places   

actual >n    rounding

actual <n    unchanged

Data input

scanf（“ character Format specification ”, Address ）;

int a, b, c;
// If you type 2 3 4
	scanf("%d%d%d",&a, &b, &c );
	printf("%d,%d,%d" ,a, b, c);

  result ：2,3,4

& Is the address character

If there is no other symbol separation for integer data input , Use space or enter

example 1： String output as is

int a, b;
	scanf("a=%d,b=%d",&a, &b );
	printf("%d,%d\n" ,a, b);

  Input format ：a=1,b=2

Otherwise, there will be an exception

example 2. Specify width output

int a, b, c;
	scanf("%1d%2d%3d",&a,&b,&c);
	printf("%d,%d,%d",a,b,c);

Input format ： 987654321

  result ：9,87,654

We can see that with the specified width, there is no need to enter the space

example 4： Real data input

float t;
scanf("%2.5f",&t);

Bear in mind ： Real data cannot specify decimal digits .

Character input and output

char a, b;
	scanf("%c%c",&a,&b);
	printf("%c,%c",a,b);

Input format ： b

  result ： ,b

Spaces are also counted as strings

Number and character assignment

char a;
	int b;
	scanf("%d%c",&a,&b);
	printf("%d,%c",a,b);

Input format ： 3a

  result ：3,a 

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Input format ： 3a

  result ：3, 

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Input format ： 10a

  result ：10,a

Be careful ：%c No space before , Character refers to a

Character input function ：getchar()

char a;
	a=getchar();
	printf("%c",a);

Input format ： a

  result ：a

Character output function ：putchar()

char a;
	a=getchar();
	putchar(a);

Compound statements and empty statements

A compound statement is a statement formed by multiple statements { }

{ } It's called a statement block , stay {} What's inside becomes a sentence .

A statement block contains multiple statements .

{
int a;
	int b;
	int c;
	int d;
}

Empty statement

;

Only semicolons “;” A statement that is composed of is called an empty statement , The system will do nothing until it is executed , And then go on ！

Empty statements are legal .

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