[Learning notes] [C Language] variable, learning notes variable

[Learning notes] [C Language] variable, learning notes variable
1. What is a variable?

When the value of a data item needs to be changed frequently or uncertain, It should be represented by a variable. For example, game points.

2. Define Variables

1> Purpose

Any variables must be defined before use.

The purpose of defining a variable is to allocate a storage space to the variable in the memory to facilitate future data storage.

If multiple variables are defined, different buckets are allocated for these variables.

2> Format

Variable name;

For example, int num;

* The variable name is an identifier.

* Variable type

* Different types of variables occupy different storage spaces. Memory is extremely limited and proper storage space is allocated

* Type of data where the constraint variable is stored (easy operation)

3. Use of Variables

1> value assignment

Save something to the variable, that is, assign values. Assign a value with a semicolon;

A = 88;

Note: The equal sign = here is not equal in mathematics, but a value assignment operator in C. It is used to assign the constant 10 on the right to variable a on the left.

The first assignment, which can be called "initialization"

Two initialization Modes

First defined, then initialized: int a; a = 10;

Initialize the definition at the same time: int a = 10;

2> modify

You can modify the value of a variable and assign values multiple times. Each assignment will overwrite the original value.

A = 10;

A = 20;

The final value of variable a is 20.

Use printf to output values of one or more variables

Int a = 10, c = 11;

Printf ("a = % d, c = % d", a, c );

Double \ float \ char output, some tips for formatting characters

 

Double height = 1.55;

Char blood = 'a ';

Printf ("height = %. 2f, blood type: % c", height, blood );

Simple addition and subtraction

Int a = 10 + 20;

* Do not use it when Initialization is not performed (the following statement is not recommended)

Int score;

Printf ("score = % d", score );

3> passing values between variables

You can assign a value to another variable.

Int a = 10;

Int B =;

Continuous assignment

A = B = 10;

4. Common Errors

1> same variable nameInt a = 10; int a = 12;

2> the variable scope is incorrect.

Variable creation and release process

Code block scope {int a = 10 ;}

5. classroom code

# Include <stdio. h> // required when printf is used

Int main ()

{

// Variable: variables should be defined to save as long as there is uncertain data

// Note that you often forget

Int score = 100;

Int time = 9;

// % D is a format character (placeholder) that can only output Integers

// \ N for line feed

Printf ("score: % d \ n", score );

Float height = 1.77f;

// % F is used to output decimal places. The default value is 6 decimal places.

Printf ("height is % f \ n", height );

// After adding. 2, the output is a 2-digit decimal number.

Printf ("height: % f.2 \ n", height );

Char a = 'a ';

// C % is used to output a character

Printf ("the value of a is % c \ n", );

Return 0;

}

Common Format characters:

1.% d or % I INTEGER (int)

2.% f decimal (float, double)

3.% c (char)