04-Constants, variables, scanf functions, and sizeof

One, constant

1. What is a constant

Constant, which represents some fixed data

2. integer constant (int) and floating-point constant (float/double)

Floating-point constants are divided into double and float two data types

* Double: dual-precision floating point, in fact, is a decimal. such as 5.43,-2.3,0.0, etc.

* float: single-precision floating-point type, also decimal, is less accurate than double , meaning that it can represent a smaller number of decimal places. In order to differentiate from double,float type data is terminated with F , such as 5.43f,-2.3f,0.0f .

3. Character constants

* Enclose a number (0~9), an English letter (a~z,a~z),or other symbols in single quotation marks. This is what constitutes a character constant. such as '6',' A ',' & ', etc.

Note: single quotes can only be extended to 1 characters, and cannot be Chinese characters.  

4. String constants

Enclose one or more characters in double quotation marks (""), which make up a string constant, such as "6"," male ".

Second, the variable

1. What is a variable

When the value of a data needs to be changed frequently, it should be represented by a variable when it gets indeterminate. Like game credits.

2. defining variables

1> Purpose

* Any variables must be defined before they can be used.

* The purpose of defining variables is to allocate a piece of storage space in memory to variables, which makes it easy to store data later.

* If more than one variable is defined, each of these variables will be allocated a different storage space

2> format

Variable type variable name;

such as int num;

* variable name belongs to identifier

* Variable type

* different types of variables occupy different sizes of storage space

* data types stored by constraint variables (easy operation)

3> examples

int Main () {    int  i;     Char C;     int A, B;     return 0 ;}

3. Use of variables

1> assigned value

i = ten;

2> Modify

* variable values can be modified and assigned multiple times.

Ten;

* output values of one or more variables using printf

int Ten  One ;p rintf ("a =%d, c =%d", A, c);

3> value passing between variables

* The value of one variable can be assigned to another variable

int Ten ; int B = A;

* Continuous Assignment

A = b = ten;  

Three, memory analysis of variables

1. byte and address

1> memory in " bytes "

0x indicates hexadecimal.

2> The bytes occupied by different types are not the same, the larger the data, the more bytes are required

2. Storage of Variables

1> bytes Consumed is related to the type of the compiler environment

2> variable Instances

int Ten ; int ;

* memory is addressed by large to small, prioritizing bytes with large memory addresses to variables. b has a larger memory address than a

* each variable has an address: the address of the first byte is the address of the variable.

3> View memory address:

int a;printf ("A's address is:%p\n", &a);

4> Note

Do not attempt to use the value of a variable before it is initialized

int a;printf ("A's value is:%d\n"//  not recommended 

Four,scanf function

1. Introduction

2. Simple usage

int age;scanf ("%d", &age);

* The scanf function waits for the user's keyboard input and does not execute the code backwards.

3. Note

do not include \ n in the first parameter of scanf , such as scanf ("%d\n", &a); This causes the scanf function to not end

Five,sizeof

1. role

used to calculate the number of bytes of memory for a variable or a constant, a data type  

2. Basic Form

* sizeof(variable \ constant)

* sizeof(data type)

Vi. break and continue

1. break

* application:switch\ cycle structure

* Break under loop nesting

2. Continue

* application: Cycle structure

* continue nested under cyclic nesting

04-Constants, variables, scanf functions, and sizeof