C language learning day_ 04

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• Learning reference B Stand on the video of teacher Hao bin , The source code in the article can be contacted by private letter if necessary .

Array

• effect
  • In order to solve the problem of storing and using a large amount of the same type of data
    • For large amounts of the same type of data , There is no need to redefine the variable name
  • To simulate the real world
    • One dimensional array ：a[x] A straight line
    • Two dimensional array ：a[x][y] The plane
    • Three dimensional array ：a[x][y][z] Space
    • Four bit array ：a[x][y][z][h] Space + Time
• Format
  • a Is a variable name.
  • n Express n A variable
  • The first is a[0], The last one is a[n-1]

a[n] = {
    1, 2, ...,n};

example ：

/* Array */
# include <stdio.h>

int main(void)
{
    
	int a[5] = {
    1, 2, 3, 4, 5};  //a Represents the array name ,5 Indicates that there are five elements 
	int i;

	for (i = 0; i < 5; ++i)
	{
    
		printf("%d\n", a[i]);
	}

	return 0;
}

• a[5] = {1, 2, 3, 4, 5}a Represents the name of the array ,5 Indicates that there are five elements , Each item is a[0]、a[1]...a[4]

/* Running results */
1
2
3
4
5
Press any key to continue

One dimensional array

• Format ：
  • int a[3];
  • It means that there is a total of 3 Elements
  • 3 The names of the elements are
    • a[0]、a[1]、a[2]
• Definition ：
  • by n Continuous allocation of storage space for variables
  • All variables must have the same data type
  • All variables must have the same byte size

/* Wrong writing 1*/
    int a[5];
    a[5] = {
    1, 2, 3, 4, 5};

• Only when you define an array can you assign a value as a whole
• After definition a[5] It is not an array , It's the first... Of the array 6 term
• Array a[5] in , Only a[0] - a[4] term , No, a[5] term

example ：a Copy the values of the array to b Array

/* Wrong writing 2*/
    b = a;  //a、b Represents the address of the first element in the array 

// Write it correctly 
    for (i = 0; i < 5; ++i)
        b[i] = a[i];

Array operation

• initialization
• assignment
• Sort
• Ask for the biggest / Small value
• The horse
• lookup
• Insert
• Delete

initialization

• Fully initialized
  • int a[5] = {1, 2, 3, 4, 5};
• Incomplete initialization
  • int a[5] = {1, 2, 3};
  • Uninitialized elements are automatically 0
• Not initialized
  • int a[5];
  • All elements are garbage values
• Zero clearing
  • int a[5] = 0
  • All elements are 0

assignment

/* Array assignment */
# include <stdio.h>

int main(void)
{
    
    int a[5];
    int i;
    
    printf(" Please enter a[0] Value ：");
    scanf("%d", &a[0]);
    printf("a[0] = %d\n", a[0]);

    printf(" Please enter a[3] Value ：");
    scanf("%d", &a[3]);
    printf("a[3] = %d\n", a[3]);
    printf("---------------\n");

    for (i = 0; i < 5; ++i)
        printf("a[%d] = %d\n", i, a[i]);  // Loop through the values of the array items 

    return 0;
}

/* Running results */
 Please enter a[0] Value ： 1
a[0] = 1
 Please enter a[3] Value ：3
a[3] = 3
---------------
a[0] = 1
a[1] = -858993460  // Items that are not initialized are filled with garbage data 
a[2] = -858993460
a[3] = 3
a[4] = -858993460
Press any key to continue

The horse

example ： Invert the elements of an array to output

/* Invert the elements of an array to output */
# include <stdio.h>

int main(void)
{
    
	int a[5] = {
    1, 2, 3, 4, 5};
	int i, j;
	int t;  // For storing temporary data 

	i = 0;
	j = 4;
	while (i < j)
	{
    
		t = a[i];
		a[i] = a[j];
		a[j] = t;

		++i;  // The global value of the variable self increasing or self decreasing is not used , therefore i++ and ++i You can use 
		--j;
	}
		
	printf(" The inverted array is output as ：");

	for (i = 0; i < 5; ++i)
		printf("%d, ", a[i]);
	printf("\n");	

	return 0;
}

/* analysis */
i = 0
j = 4

0 < 4 establish , Into the loop 

t = a0 = 1
a0 = a4 = 5
a4 = t = 1

i = 1
j = 3

1 < 3 establish , Into the loop 

t = a1 = 2
a1 = a3 = 4
a3 = t = 2

i = 2
j = 2

2 < 2 Don't set up , Exit loop 

a[5] ={
    5, 4, 3, 2, 1}  //a[2] Value does not change 

/* Running results */
 The inverted array is output as ：5, 4, 3, 2, 1,
Press any key to continue

• Test whether even numbers still hold

Two dimensional array

• Format ：
  • int a[3][4];
  • It means that there is a total of 12 Elements , Can be viewed as 3 That's ok 4 Look at
  • 12 The names of the elements are ：

a[0][0]  a[0][1]  a[0][2]  a[0][3]
a[1][0]  a[1][1]  a[1][2]  a[1][3]
a[2][0]  a[2][1]  a[2][2]  a[2][3]

• a[i][j] It means the first one i + 1 That's ok , The first j + 1 Column

2D array initialization

• The two ways are equivalent

/* 2D array initialization */
    int a[3][4] = {
    1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}
    int a[3][4] = {
    
        {
    1, 2, 3, 4},
        {
    5, 6, 7, 8},
        {
    9, 10, 11, 12}
    };

Two dimensional array operation

• Output to two-dimensional array
• Sort 2D arrays
• Find the maximum value of each line
• Judge whether the matrix is symmetrical
• Multiplication of matrices

/* Two dimensional array representation and output */
# include <stdio.h>

int main(void)
{
    
    int a[3][4] = {
    
        {
    1, 2, 3, 4},
        {
    5, 6, 7, 8},
        {
    9, 10, 11, 12}
    };

    // You can also enter a two-dimensional array as follows 
    //int a[3][4] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};

    int i,j;

    for (i = 0; i < 3; ++i)
    {
    
        printf(" The first  %d  That's ok ：", i + 1);
        for (j = 0; j < 4; ++j)
        {
    
            printf("%-3d", a[i][j]);  //-3d% Indicates left alignment , Intermediate proportion 3 The position of the cursor 
        }
        printf("\n");
    }

    return 0;
}

/* Running results */
 The first  1  That's ok ：1  2  3  4
 The first  2  That's ok ：5  6  7  8
 The first  3  That's ok ：9  10 11 12
Press any key to continue

Whether there is a multidimensional array

• There is no multidimensional array
  • Because memory is linear and one-dimensional
• n The dimension group can be regarded as n - 1 One dimensional array of dimension groups
  • int a[3][4];
    • The array contains 3 One dimensional array of elements
    • Each one-dimensional array can also contain 4 Elements

【 Article source code reference GitHub】

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 All of the above are original , If unknown or wrong , Please point out .

The author of this article ： Bad

Link to this article ： https://blog.csdn.net/qq_45668124/article/details/115090798

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