Small turtle C (Chapter 6 arrays 1 and 2)

The concept of array

Array ： A sequence of data of the same type , It's an ordered set .

Each data in the array is called ： Array elements , Subscript element

Array elements    It is numbered by its location （ Call the subscript of the array element ） To distinguish between .

With array name and subscript   All elements in the array can be processed in a unified way , Thus, it is convenient to deal with a batch of data with the same nature .

Be careful ： Array element order does not mean element size order .

Definition and reference of one dimensional array

The definition of one-dimensional array ： stay C The use of arrays in languages must be defined first .

                                    Type specifier Array name [ Constant expression ];       

                                     for example ：int a [10]  It means that an array of integers is defined , Array name a, This array has 10 Elements ,10 Each element is an integer variable .

It should be noted that ：

One 、 A type specifier is any basic or constructive data type . For the same array , All data elements of the same type .

Two 、 The array name is a user-defined array identifier . The writing rules should conform to the writing rules of identifier .

3、 ... and 、 The constant expression in square brackets represents the number of data elements , It also becomes the length of the array .

Four 、 Allow in the same type description , Describes multiple arrays and variables . for example ：int a,b,c,d,k1[10],k2[20];

Some common mistakes ：

①float a[0];     // The array size is 0 It makes no sense

②int b(2)(3);   // You can't use parentheses

③int k,a[k];     // You cannot use variables to describe the number of groups

A reference to one-dimensional array elements

Array elements are the basic elements of an array . Array elements are also variables , Its identification method is array name followed by a subscript . The subscript indicates the order number of the elements in the array .

The general form of array elements is ： Array name [ Subscript ]    （ Subscripts can be integer constants or integer expressions ）

for example ：a[0]=a[5]+a[7]-a[2*3]     a[i+j]     a[i++]      Are all legal array elements

Some precautions ：

Array elements are often referred to as subscript variables . You have to define the array first , To use subscript variables . stay C Subscript variables can only be used one by one in a language , Instead of referring to the entire array at once .

The following is wrong ：printf("%d",a);

When defining an array “ Array name [ Constant expression ]” And references to array elements “ Array name [ Subscript ]” There is a difference .

for example ：int a[10];   // Define the array length as 10

           t=a[6];      // quote a The sequence number in the array is 6 The elements of . here 6 Does not represent array length .

Initialization of one dimensional array

In addition to using assignment statements to assign values to array elements one by one , Initialization and dynamic assignment can also be used .

Array initialization assignment refers to giving initial values to array elements when defining an array . Array initialization is done in the compile phase . This reduces running time , Increase of efficiency .

Be careful ： Previously, you can also specify the initial value of the array number with an assignment statement or an input statement , It's done at run time .

The general form of initialization assignment is ：

Type specifier Array name [ Constant expression ]={ value , value ,...... value };

There are several ways to initialize one-dimensional arrays ：

（ One ） When defining an array, assign initial values to the elements of the array , for example ：int a [10]={0,1,2,3,4,5,6,7,8,9};

Put the initial values of the array elements in a pair of flower brackets in turn . After the above definition and initialization ,a[0]=0,a[1]=1,a[2]=2,......,a[8]=8,a[9]=9.

（ Two ） You can assign values to just a few elements , for example ：int a [10]={0,1,2,3,4};

Definition a Array has 10 Elements , But only 5 An initial value , This means only to the front 5 Each element has its initial value , after 5 Elements are 0.

（ 3、 ... and ） If you want all the elements in an array to be 0, It can be written. int a[10]={0,0,0,0,0,0,0,0,0,0}; or int a [10]={0};

  ( Four )  When assigning initial values to all array elements , Because the number of data has been determined , Therefore, the array length can not be specified .

for example ：int a [5]={1,2,3,4,5}; Or you could write it as ：int a [ ]={1,2,3,4,5};

In the second way , There are in parentheses 5 Number , The system will define it automatically a The length of the array is 5. But if the array length is different from the number of initial values provided , Array length cannot be omitted . for example , Suppose the length of the array is 10, We can't omit the definition of array length , It must be written as int a [10]={1,2,3,4,5}; Only before initialization 5 Elements , after 5 Elements are 0. 

（ 5、 ... and ） Dynamic assignment