C language -- array

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Preface

Hello everyone , Today, let's talk about simple knowledge about arrays .

One 、 What is an array ？

An array is a collection of data of the same type in a continuous space .
int a = 0;// This is an integer variable
When we just need to store 5 Of course, we can create data 5 A variable ,
But if we want to count the whole class 50 The results of three students , Then let's create it again 50 Variables are not so convenient ,
Upward, we should count the whole school 2000 Students' grades ？ At this time, just naming is enough for us to have a headache ,
At this time, the simplicity of the array is reflected
The code is as follows （ Example ）：

int arr[50] = {
     0 };// Be able to store 50 An array of shaped data 
int arr[2000] = {
     0 };// Deposit 2000 There's a plastic data 

1、 Arrays can be created of any type , for example ：int,char,double etc.
2、 Arrays can be accessed by subscripts , The subscript operator is ：[ ];
What needs to be noted here is The subscript of an array is from 0 At the beginning ,
That is to say, create an array ： int arr[5] = { 0 };
arr[0] Is the first element of the array ,arr[1] Is the second element of the array ,
And so on , The last element of the array is arr[4] instead of arr[5]

3、 Array elements are stored in a contiguous memory space
We need to use Fetch address operator ：&（ Get the first address of the storage space of the variable in memory ）;
Pictured &arr[0] = 0xE33AF450;（0x Beginning with 16 Base number ）
As you know, an integer variable takes up four bytes , So every next element , Its first address will increase 4

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Two 、 Exercises ：

1. seek 10 The highest score among students

The code is as follows （ Example ）：

#include<stdio.h>
int main() {
    
	int arr[10] = {
     0 };
	puts(" Please enter 10 Scores of students .");//puts(""); Output string and wrap 
	
	int i = 0;
	for (i = 0; i < 10; i++) {
    
		printf("arr[%d] = ", i);
		scanf("%d", &arr[i]);
	}
	
	int max = arr[0];// Assign the first student's grades to max
	for (i = 1; i < 10; i++) {
    // Start with the second student 
		if (max < arr[i])
			max = arr[i];
	}
	printf(" The highest score is ：%d\n", max);
	return 0;
}

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2. Yes 5 Students' grades are sorted in ascending order

The code is as follows （ Example ）：

#include<stdio.h>

int main() {
    
	int arr[5] = {
     0 };
	int i = 0;
	puts(" Please enter 5 Scores of students .");
	for (i = 0; i < 5; i++) {
    
		printf("arr[%d] = ", i);
		scanf("%d", &arr[i]);
	}

	for (i = 0; i < 4; i++) {
    	// Bubble sort 
		for (int j = 0; j < 5 - 1 - i; j++) {
    
			if (arr[j] > arr[j + 1]) {
    
				int z = arr[j];
				arr[j] = arr[j + 1];
				arr[j + 1] = z;
			}
		}
	}
	
		puts(" Ascending by bubble sorting .");
		for (i = 0; i < 5; i++) 
			printf("arr[%d] = %d\n", i, arr[i]);
		printf("\n");
	return 0;
}

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3、 ... and 、 Particular attention ：

1. There are two special cases of the use of array names
The first is sizeof（ Array name ）, The array name here represents the whole array , The result is the number of bytes occupied by the entire array
The second is & Array name , The array name here represents the address of the whole array , Find the address size of the entire array
In addition to the above two cases , Other array names represent the address of the first element .

2.int arr[] = {0, 1, 2, 3, 4};
The size of the array is omitted during initialization here , The compiler will automatically initialize the array size according to the number of data we initialize ,
Initialize here as arr[5].
It can be seen that the number of arrays can be omitted , But pay attention to the omission of multidimensional arrays
for example ：int arr[3][4] = { 0 }; This is an array with three rows and four columns , We can think of it as the element type int [4], The number of elements is 3 Array of
Here, the number of elements can also be omitted and written as int arr[ ][4] = { 1,2,3,4,5,6 }; At this time, the number of elements is 2
In the same way int arr[ ][4][5] = { 1,2,3,4,5,6 }; Element type is int [4][5] , The number of elements is 1
But attention should not be written int arr[3][] = { 1,2,3,4,5,6 }; Writing in this way means that the element type is ambiguous , The compiler doesn't know how to allocate these integers .

3. When an array is passed as a parameter, the first address of the element is passed , Not the whole array
So if you use sizeof(arr）/ sizeof(arr[0]) In this way, the number of elements cannot be calculated ,
When an array is passed as a parameter, it is impossible to pass the entire array , So if you need to count the number of elements and send them out when passing parameters .

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summary

The first part of today is about the most basic knowledge of arrays , The third part is more difficult , We will discuss in detail in the next blog ,
That's it today , Thank you. .