[C language] one dimensional array

​ The concept and use of arrays

We want to put data into memory space , First, you must allocate memory space . So we put in ⑤ individual

int

  The value of the memory space of type , for example ：

int

 

arr [5];

This allocates... In memory ⑤ individual  

int

  Type of memory space , common  4×5=20  Bytes , And gave them a name , It's called

arr.

• Each element in the array has a sequence number , This number comes from  
  0
    Start , Not from the familiar  
  1
    Start , It's called subscript  
  （Index）
   . When using array elements , Indicate the subscript , for example ：

• arrname
   
  [Index]

• arraName  Is the array name ,index  Subscript . for example ：a[0]  It means the first one 1 Elements ,a[3]  It means the first one 2 Elements .

• When using arrays , We often use the elements in the array , however   Then print out the values in turn  ( That is to assign initial values to the elements in the array one by one ). Then use the loop structure to output （ That is, read the values of array elements in turn ） As shown in the following code ：

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main(void)
{
 int i;
 int arr[10] = { 0 };
 for (i = 0; i < 10; i++)// take 1~10 Put it in the array
 {
 arr[i]=(i+1);
 }
 for (i = 0; i < 10; i++)
 {
 printf(&quot;arr[%d] = %d\n&quot;, i, arr[i]);// Output the array in turn
 }
 return 0;
}


Running results ： as follows

​​

Variable  

i

  Is an array subscript , It's also --> The loop condition ; Use array subscripts as loop conditions , When the last element is reached, the loop ends . Array  

arr

  The largest subscript of is  

9

, That is, no more than  

10

, So we specify that the condition of the cycle is  

i<10

, once  

i

  achieve  

10

  You have to end the cycle .

• So let's change the code above ： Let the user enter ten numbers ！ The code example is as follows ：

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main(void)
{
 int i;
 int number[10] = {0};
 printf(&quot;| Please enter ten numbers :|\n&quot;);
 for (i = 0; i < 10; i++)
 scanf(&quot;%d&quot;, &number[i]);
 for (i = 0; i < 10; i++)
 printf(&quot;%d &quot;, number[i]);
 return 0;
}


Running results ： as follows ：

​​

Array name

• The array name is
  First element
  The address of . But there are
  ②
  Exceptions ：

• sizeof( Array name ) ——>&nbsp;  The array name represents the entire array  —  It calculates the size of the entire array , Unit is byte .

• Address fetch (&)  Array name  ——>&nbsp;  The array name represents the entire array  —  It takes out the address of the entire array .

The definition of one-dimensional array

A one-dimensional array is used to store a set of data in a bit sequence . Its general form is as follows ：

Type specifier &nbsp; &nbsp;  Array identifier  [ Constant expression ];

• The type specifier represents ： The type of all elements in the array , Is any basic data type or construction type .

• The array identifier represents ： The name of the array type variable , The naming rules are consistent with the identifier of the variable name . This is also called , Array identifier .

• A constant expression represents ： Defines the number of data elements stored in the array , That is, the length of the array .

• int a[10];
  &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; explain   integer   Array  a, Yes  10  Elements .

• float b[10],c[20];
  &nbsp;  explain   Single precision floating point   Array  b, Yes  10  Elements , Real array  c, Yes  20 Elements .

• char ch[20];
    Description character array  ch, Yes  20  Elements

A reference to a one-dimensional array

• After the array definition is completed , Use this array . You can use the elements of an array by referencing them . Be careful ： The index to access the array is from
  0
  At the beginning .

The general form of an array is defined as follows ：

• Array identifier  
  [ Subscript ]

for example ： Reference an array variable  

arr

  pass the civil examinations

②

A variable .

• arr 
  [2];

Find out the total size of the array elements is ：

int sz = sizeof(arr) / sizeof(arr[0]);

Examples of related topics , as follows ：

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main(void)
{
 int i = 0;
 int arr[10] = { 0 };
 int sz = sizeof(arr) / sizeof(arr[0]);// Calculate the total element size of the array
 arr[5] = 5;
 arr[6] = 7;
 for (i = 0; i < sz; i++)
 {
 printf(&quot;%d &quot;, arr[i]);
 }
 return 0;
}


The following example shows the results of running ：

​​

🥏 There are a few things to note about arrays ：

• The array is being created ,【】 Give a constant in parentheses , You can't use variables ！ Be careful ： Out-of-service  
  const
    Keyword decoration is given to it , Its essence is still
  Variable .

• In the array , for example ：arr[5]  Can only be used in  arr[0]、arr[1]、arr[2]、arr[3]、arr[4], They can't be used  arr[5]. If you use it  arr[5], Will lead to
  The subscript crossing the line
  The situation of .

• The subscript can be  
  Integer constant
    Or is it  
  Shaping expression
  .

• The type of array actually refers to the value type of array elements . For the same array , The data types of all its elements are
  same
  .

• String words , Array subscript is the character that only knows your array subscript , barring  
  '\0'
   .

Initialization of one dimensional array

• In addition to using assignment statements to assign values to array elements one by one , Initialization assignment and dynamic assignment methods 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 will reduce running time , Increase of efficiency .

• int a = 10;
  &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; //  initialization

• int arr[5] = {1,2,3,4,5};
  &nbsp; //  Fully initialized

• int arr1[5] = {1,2,3};
   &nbsp; &nbsp; &nbsp; //  Incomplete initialization , Incomplete initialization , The remaining uninitialized elements  
  The default is 0

​​

• If your subscript does not specify a subscript , It will see how many elements you have by default, so as to help you determine the subscript of the array .

• int arr[] = {1,2,3,4,5};

• int arr[5] = {1,2,3,4,5};

• above ② Sentence codes are completely equivalent ！！！ It will be initialized according to the following data , To determine the subscript of the array ！

One dimensional array memory storage mode

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main(void)
{
 int i = 0;
 int arr[10] = { 0 };
 int sz = sizeof(arr) / sizeof(arr[0]);
 for (i = 0; i < sz; i++)
 {
 //%p -  Print in address format , In hexadecimal ！
 printf(&quot;arr[%d] = %p\n&quot;, i, &arr[i]);
 }
 return 0;
}


Running results ： as follows

​​

• One dimensional arrays are stored continuously in memory ！

• As the array subscript grows , The address changes from ground to height ！

🥏 practice ： Use a one-dimensional array to save student names ！

This code uses --->  Pointer array operation ！

#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main(void)
{
 int i; // Control loop variable
 char *Arrname[5] = { 0 }; // Character pointer array
 // Indirect addressing through dereference operation
 Arrname[0] = &quot; name : Zhang San &quot;;
 Arrname[1] = &quot; Gender : male &quot;;
 Arrname[2] = &quot; Telephone :[phone]&quot;;
 Arrname[3] = &quot; Student number :0&quot;;
 Arrname[4] = &quot; Address : The earth &quot;;

 for (i = 0; i < 5; i++)
 {
 printf(&quot;%s\n&quot;, Arrname[i]);
 printf(&quot;\n&quot;);
 }
 return 0;
}


Running results ： as follows

​

​