Su embedded training - day4

One 、 Array

1.1 The concept of array

Array ：
Save a set of data of the same type
Whether it's a multi-dimensional array , Is to open up a continuous memory space
Array is a construction data type （ Array , Structure , Shared body ）

1.2 One dimensional array

1.2.1 The definition of one-dimensional array

< Storage type > < data type > < Array name > [ The array subscript ]
 Storage type ：auto,register,static,extern
 data type ： Basic data type ：int,char,float.... etc. 
 Array name ： Is an identifier , Meet the naming rules of identifiers 
 The array subscript ： Determine the number of elements in the array 
 for example ：
int a[10];
 meaning ： Define a name a Array of , altogether 10 Elements , Every element is int type .

1.2.2 Properties of one-dimensional array

#include <stdio.h>

int main(int argc, const char *argv[])
{
	int a[4];
	a[0] = 222;
	a[1] = 333;
	a[2] = 444;
	a[3] = 555;
	printf("%d %d %d\n",a[0],a[1],a[2]);
	// When defining and using arrays , Try not to use variables in the following table of array 
	// Prevent later variable changes from affecting the operation of the array , Generally, array subscripts are constants or constant form Masters , The macro definition itself is also a constant expression , So it can be used as an array subscript 
#if 0
	int num = 10;
	int b[num];
	b[2] = 5;
	int n =3;
	b[n] = 888;
	printf("%d %d\n",b[2],b[n]);
#endif
	printf("sizeof(a) = %ld %ld\n",sizeof(a),sizeof(int)*4);

	printf("%p\n",&a[0]);
	printf("%p\n",&a[0]+1);
	printf("%p\n",a);
	printf("%p\n",a+1);
	printf("%p\n",&a);
	printf("%p\n",&a+1);
	a++;  // Array names are constant pointers , Do not modify 
	return 0;
}

1.3 Initialization and traversal of one-dimensional array

1. All initialization 
2. Local initialization 
3. Initialize all without specifying array subscripts 

#include <stdio.h>

int main(int argc, const char *argv[])
{
	// If you define an array inside a function without initializing , Then every element is a random value 
	//int a[5];
	//a = {1,2,3,4,5};  // Wrong writing 
	// All initialization 
	//int a[5] = {1,2,3,4,5};
	//int a[5] = {0};  // All initialized to 0
	//int a[5] = {};  // Some compilers do not support this writing 
	//int a[5] = {1,2,3};  // Local initialization , Elements without assignment are automatically initialized to 0
	int a[] = {1,2,3,4,5,6,7};  // Do not specify array subscript , The system will set the array subscript according to the number of initialized data 
	printf("sizeof(a) = %ld\n",sizeof(a));


	/* One dimensional array traversal */
	int i;
	for(i = 0 ; i < sizeof(a)/sizeof(a[0]);i++)
	{
		printf("%d ",a[i]);
		//printf("a[%d] = %d\n",i,a[i]);
	}
	putchar(10);
	return 0;
}

1.4 Bubble sort

#include <stdio.h>


int main(int argc, const char *argv[])
{
	int a[10] = {0};
	printf(" Please enter 10 A digital ：\n");
	int i,j;
	int length = sizeof(a)/sizeof(a[0]);
	for(i = 0 ; i < length;i++)
	{
		scanf("%d",&a[i]);
	}
	for(i = 0 ; i < length - 1;i++)
	{
		for(j = 0 ; j < length - 1 - i;j++)
		{

			if(a[j] < a[j+1])
			{
#if 0
				int t = a[j];
				a[j] = a[j+1];
				a[j+1] = t;
#endif
			a[j] = a[j] + a[j + 1];
			a[j + 1] = a[j] - a[j + 1];
			a[j] = a[j] - a[j + 1];
			}
		}
	}
	for(i = 0 ; i < length;i++)
	{
		printf("%d ",a[i]);
	}
	putchar(10);
	return 0;
}

Two 、 Two dimensional array

2.1 Definition and properties of two-dimensional array

 Storage type   data type   Array name  [ Row number ][ Number of columns ];
 for example ：int arr[3][4];

#include <stdio.h>

int main(int argc, const char *argv[])
{
	int a[2][3] = {
   {1,2,3},{4,5,6}};
	//int a[2][3] = {
   {1},{4,5}};
	//int a[][3] = {
   {1,2,3},{4,5,6}};
	//int a[][3] = {1,2,3,4,5,6,7,8};
	//int a[2][3] = {0};
	int i,j;
	for(i = 0;i < 3;i++)
	{
		for(j =0 ; j < 3;j++)
		{
			printf("a[%d][%d] = %d\n",i,j,a[i][j]);
		}
	}

	printf("%p\n",&a[0][0]);
	printf("%p\n",&a[0]);
	printf("%p\n",a);
	printf("%p\n",&a);

	printf("%p\n",&a[0][0] + 1);
	printf("%p\n",&a[0] + 1);
	printf("%p\n",a + 1);
	printf("%p\n",&a + 1);

	return 0;
}

2.2 Initialization and traversal of two-dimensional array

#include <stdio.h>

int main(int argc, const char *argv[])
{
	//int a[3][4];
	//int a[2][3] = {
   {4,5,6},{7,8,9}};// All initialization 
	//int a[2][3] = {1,2,3,4};   // Store by line , There is no set auto fill 0
	//int a[2][3] = {
   {1},{2}};
	//int a[][3] = {
   {10,20},{30}};
	//int a[2][] = {1,2,3,4,5};  // Wrong writing 
	int i,j;
	// The outer loop controls the number of lines 
	// The number of inner loop control columns 
	for(i = 0 ; i < 2;i++)
	{
		for(j = 0 ; j < 3;j++)
		{
			printf("%-5d",a[i][j]);
		}
		putchar(10);
	}

	return 0;
}

3、 ... and 、 Character arrays and strings

A character array ： Every element stored in the array is a character
A string is essentially an array of characters

#include <stdio.h>

int main(int argc, const char *argv[])
{
	char ch1[] = {'h','e','l','l','o'};
	printf("sizeof(ch1) = %ld\n",sizeof(ch1));
	// Traversal of character array 
	int i;
	for(i = 0; i < sizeof(ch1)/sizeof(ch1[0]);i++)
	{
		printf("%c ",ch1[i]);
	}
	putchar(10);
	char ch2[] = "world";
	printf("sizeof(ch2) = %ld\n",sizeof(ch2));

	printf("ch2 = %s\n",ch2);
	
	char ch3[] = {'h','e','l','l','o','\0'};
	printf("ch3 = %s\n",ch3);
	
	char ch4[] = "hello\0world";
	printf("sizeof(ch4) = %ld\n",sizeof(ch4));
	for(i = 0 ; i < sizeof(ch4)/sizeof(ch4[0]);i++)
	{
		printf("[%c] %d\n",ch4[i],ch4[i]);
	}
	puts("---------------------------------------");
	char str[4][32] = {"hello","nihao beijing","hello kitty","welcome to nanjing"};
	int j;
	for(i = 0 ; i < 4;i++)
	{
		for(j = 0 ; j < 32;j++)
		{
			printf("%c",str[i][j]);
		}
		putchar(10);
	}
	return 0;
}

3.1 Reverse string order

#include <stdio.h>

int main(int argc, const char *argv[])
{
	char str[32] = {0};
	printf(" Please enter a string : ");
	scanf("%s",str);

	int i = 0,length = 0;
	while(str[i] != '\0')
	{
		length++;
		i++;
	}
	int x = 0, y = length -1;
	for(i = 0 ; i < length /2 ;i++)
	{
		char t = str[x];
		str[x] = str[y];
		str[y] = t;

		x++;
		y--;
	}
	printf("%s\n",str);
	return 0;
}

3.2 insert data

Enter a string , Location , The elements inserted

#include <stdio.h>
#include <string.h>
int main(int argc, const char *argv[])
{
	char str[32] = {0};
	int num,i;
	char ch;
	printf(" Please enter the string , Location , The elements inserted :\n");
	scanf("%s%d %c",str,&num,&ch);
	int length = strlen(str);
	for(i =0 ; i < length - num +1;i++)
	{
		str[length - i] = str[length -i - 1];
	}
	str[num - 1] = ch;
	printf("%s\n",str);
	return 0;
}

Four 、 String function

4.1 Why use string functions

Generally, strings are stored in an array , But after the array is defined , It cannot be operated as a whole , So we need to operate on strings with the help of string related functions

#include <stdio.h>
int main(int argc, const char *argv[])
{
	char s1[] = "hello world";
	char s2[] = "hello world";
	if(s1 == s2)
	{
		printf("s1 = s2\n");
	}
	else
	{
		printf("s1 != s2\n");
	}
	// If the array is not initialized , Array subscript must be written 
	//char str[];
	return 0;
}

4.2 Common string functions

4.2.1 strlen()

 The header file ：#include <string.h>
       
 Prototype ：size_t strlen(const char *s);
 function ： Get the length of a string 
 Parameters ：s: To get a string of length 
         Pass in a string directly , Or character array names 
 Return value ： Length of string 

#include <stdio.h>
#include <string.h>

int main(int argc, const char *argv[])
{
	//strlen Function to get the length of the string 
	// The length obtained is the first in this string \0 Length before position , barring \0
	char s1[] = "hello world";
	printf("strlen(s1) =%ld\n",strlen(s1));
	printf("sizeof(s1) =%ld\n",sizeof(s1));

	char s2[] = "hello wor\0ld";
	printf("strlen(s2) =%ld\n",strlen(s2));
	printf("sizeof(s2) =%ld\n",sizeof(s2));
	// The following is not a string , No, \0, So it can't be used strlen To get the string length ,strlen I will always look for it from the first address \0
	char s3[] = {'h','e','l','l','o'};
	printf("strlen(s3) =%ld\n",strlen(s3));
	printf("sizeof(s3) =%ld\n",sizeof(s3));
	
	char s4[32] = "hello world";
	printf("strlen(s4) =%ld\n",strlen(s4));
	printf("sizeof(s4) =%ld\n",sizeof(s4));
	return 0;
}

4.2.2 strcmp()

 The header file ：#include <string.h>
       
 Prototype ：int strcmp(const char *s1, const char *s2);

 function :  Compare the size of two strings 
 Parameters ：s1,s2 Two strings 
 Return value ：
    0： s1 = s2
    <0: s1 < s2
    >0: s1 > s2
int strncmp(const char *s1, const char *s2, size_t n);
 Used to compare two strings before n Whether the two bytes are the same 

#include <stdio.h>
#include <string.h>
int main(int argc, const char *argv[])
{
	//strcmp The comparison is \0 Previous content , It has nothing to do with the memory space of the string 
	//char s1[32] = "hello w\0orld";
	//char s2[] = "hello w\0orld";
	char s1[] = "h";
	char s2[] = "hello abcdefgwhi";

	int ret = strcmp(s1,s2);
	if(ret == 0)
	{
		printf("s1 = s2\n");
	}
	else if(ret > 0)
	{
		printf("s1 > s2\n");
	}
	else
	{
		printf("s1 < s2\n");
	}

	int k = strncmp(s1,s2,2);
	if(k == 0)
	{
		printf("s1 = s2\n");
	}
	else if(k > 0)
	{
		printf("s1 > s2\n");
	}
	else
	{
		printf("s1 < s2\n");
	}

	return 0;
}

4.2.3 strcpy()

 The header file ：#include <string.h>
       
 Prototype ：char *strcpy(char *dest, const char *src);

 function :  take src The string is assigned to dest In a string 
 Parameters ：
    dest: Destination string 
    src: The source string 
 Return value ：
     Return the first address of the destination string 
char *strncpy(char *dest, const char *src, size_t n);

#include <stdio.h>

#include <string.h>
int main(int argc, const char *argv[])
{
	char s1[32];
	strcpy(s1,"hello world");
	printf("s1 = %s\n",s1);

	char s2[] = "hello world";
	char s3[32] = "abcdefg";
	//strcpy take  s3 The first of \0 Copied to s2
	strcpy(s2,s3);
	printf("sizeof(s2) = %ld\n",sizeof(s2));
	printf("s2 = %s\n",s2);

	int i;
	for(i = 0 ; i < sizeof(s2)/sizeof(s2[0]);i++)
	{
		printf("[%c] %d\n",s2[i],s2[i]);
	}
	puts("------------------------");
	char buf1[32] = "hello world";
	char buf2[32] = "abcdefghijklmnopqrsst";
	//strcpy(buf1,buf2);
	// Is the first of the second parameter n Bytes are copied to the first parameter 
	strncpy(buf1,buf2,7);
	printf("buf1 = %s\n",buf1);
	return 0;
}

5.2.4 strcat()

 The header file ：#include <string.h>
       
 Prototype :char *strcat(char *dest, const char *src);

 function :  take src Append to dest Behind 
 Parameters ：
    dest: Destination string 
    src: The source string 
 Return value ：
     The first address of the appended string 
char *strncat(char *dest, const char *src, size_t n);

#include <stdio.h>
#include <string.h>
int main(int argc, const char *argv[])
{
	char s1[32] ="hello wo\0rldadadjajdalsdkjaskdj";  //hello woabcdefg\0
	char s2[32] ="abcdefg\0higk";

	strcat(s1,s2);
	printf("s1 = %s\n",s1);
	return 0;
}

5.2.5 Realize it by yourself strcpy Function functions

#include <stdio.h>

char *my_strcpy(char *s1,char *s2)
{
    if(NULL == s1 || NULL == s2)
    {
	return NULL;
    }

    int i = 0;
    while(s2[i] != '\0')
    {
	
	s1[i] = s2[i];
	i++;
    }
    s1[i] = '\0';
    return s1;
}

int main()
{
    char s1[] = "hello world";
    char s2[] = "world";

    char *result = my_strcpy(s1,s2); 
    
    for(int i = 0; i < sizeof(s1)/sizeof(s1[0]); i++)
    {
	printf("[%c] %d\n",result[i],result[i]);
    }

    return 0;
}

6、 ... and 、 The pointer

6.1 The purpose of the pointer

 The application procedure is simple , compact , Efficient 
 Effectively represent complex data structures 
 Dynamic memory allocation 
 Get the return value of more than one function 

6.2 The concept of pointer

When a variable is defined in the program , The program will open up memory space in memory for this variable , Every byte of space in our memory has a number , Call this number address , Addresses are also called pointers

Without affecting understanding , Sometimes the address , The pointer , Pointer variables do not distinguish , Generic pointer
&: Fetch address
*：
1. Definition time , If the front is a type , Indicates that this is a definition statement , Define a pointer variable ,pa It's a pointer , Point to integer a
2. When using ,*pa = 100;* It means to take a value , Take the pointer pa The value of the memory pointed to
pa = Address

#include <stdio.h>

int main(int argc, const char *argv[])
{
	//int a = 1;
	//int *pa = &a;
	printf("int* = %ld\n",sizeof(int *));
	printf("char* = %ld\n",sizeof(char *));
	printf("double* = %ld\n",sizeof(double *));
	printf("float* = %ld\n",sizeof(float *));
	printf("long* = %ld\n",sizeof(long *));
	
	int a = 1;
	char ch = 'a';
	//int *pc = &ch;  // incompatible types 
	char *pch = &ch;
	
	//ch = 'x';
	*pch = 'x';  // Equivalent to ch = 'x'
	printf("ch = %c\n",ch);
	printf("ch = %c\n",*pch);
	int *pa = &a;
	printf("%p\n",pch);
	printf("%p\n",pa);
	
	printf("%p\n",pch + 1);  // Different types of pointers , Different steps 
	printf("%p\n",pa + 1);
	return 0;
}

6.3 Operation of pointer variable

Pointer operation takes the address stored in pointer variables as the operation quantity .
therefore , The essence of pointer operation is the operation of address .
The types of pointer operations are limited , It can only perform arithmetic operations , Relation operation and assignment operation

6.3.1 Arithmetic operator

+：  px + n  The pointer moves in the direction of the larger address n Data  
-：  px - n  The pointer moves in the direction of small address n Data 
++： px++    The pointer moves in the direction of the larger address 1 Data 
--： px++    The pointer moves in the direction of small address 1 Data 

Pointer variable addition and subtraction , Indicates that the pointer variable moves in the direction of large or small address N Operation space , Subtract two pointer variables , Indicates how many operation spaces there are between two addresses （ How many elements ）
Be careful , Two pointers do operations , Must be of the same type , Different types make no sense .
Adding and subtracting a pointer variable makes sense , Multiplication and division are meaningless

 After ++ Priority is higher than the front ++
 After ++ The law of union goes from left to right 
 In front of ++ and * Same priority , The law of union goes from right to left 

#include <stdio.h>

int main(int argc, const char *argv[])
{
	int arr[6] = {1,3,5,8,9,10};
	int *p1 = arr;
	printf("*p1 = %d\n",*p1);
	p1++;
	int *p2 = p1++;
	printf("*p1 = %d,*p2 = %d\n",*p1,*p2);
	printf("p1 - p2 = %ld\n",p1 - p2);

	int y = *p1;  // Value 
	printf("y = %d\n",y);
	y = ++*p1;
	printf("y = %d\n",y);
	y = (*p1)++;
	printf("y = %d\n",y);
	
	y = *p1++;   // When the assignment is complete , The pointer px Add 1
	printf("y = %d\n",y);
	printf("*p1 = %d\n",*p1);
	/*y = ++*p1++;   // When the assignment is complete , The pointer px Add 1
	printf("y = %d\n",y);
	printf("*p1 = %d\n",*p1);
	*/
	
	return 0;
}

6.3.2 Relational operator

>     px > py
<
>=
<=
!=
==

Two pointer variables can determine the size of the save address through relational operators
The relational operator between two pointers represents the relationship between the address positions they point to , The pointer pointing to a large address is larger than the pointer pointing to a small address
The relation operation between pointers with different data types is meaningless , Between two pointers of data pointing to different data areas , Relational operators are meaningless .
The relation operation between pointer and general integer variable is also meaningless , But we can do equal or unequal relation operation with zero , Determine if the pointer is empty , Generally speaking, it is related to NULL

6.3.3 The assignment operation

Pointer variables can be assigned directly , But you cannot assign an integer to a pointer variable , Because there is no open space
Pointer assignment operation is to send an address value to pointer variable through assignment operator ,

6.2.4 practice ： Enter a string , Flip the elements of the string

#include <stdio.h>
#include <string.h>
int main(int argc, const char *argv[])
{
	char str[32] = {0};
	gets(str);
	printf(" Reverse the previous string ：%s\n",str);

	char *p = NULL,*q = NULL;
	char tmp;
	p = &str[0];
	q = &str[strlen(str) - 1];
#if 0
	while(p < q)
	{
		tmp = *p;
		*p = *q;
		*q = tmp;
		p++;
		q--;
	}
#endif
	for(;p < q;p++,q--)
	{
		tmp = *p;
		*p = *q;
		*q = tmp;
	}
	printf(" The inverted string ：%s\n",str);


	return 0;
}

7、 ... and 、 Pointers and one-dimensional arrays

#include <stdio.h>
#include <string.h>

int main(int argc, const char *argv[])
{
	int a[5] = {1,2,3,4,5};
	int *p = a;
	int i;
	for(i = 0 ; i < 5;i++)
	{
		//printf("%d ",a[i]);
		printf("%d ",*(p+i));
	}
	putchar(10);


	char *s = "helloworld";
	char str[32] ="hello nanjing";
	s = str;
	//printf("%s\n",s);
	for(i = 0 ; i < 10;i++)
	{
		printf("%c",s[i]);
	}
	putchar(10);
	return 0;
}

practice

practice 1： Realize by yourself through pointer strlen Function functions

#include <stdio.h>

int main(int argc, const char *argv[])
{
	char buf[32] = {0};
	printf(" Please enter a string ：\n");
	gets(buf);
	char *p = buf;
	int i;
	while(*p != '\0')
	{
		p++;
		i++;

	}
	printf("strlen(buf) = %d\n",i);
	return 0;
}

practice 2： By pointer strcpy Function functions

#include <stdio.h>

int main(int argc, const char *argv[])
{
	char s1[] = "helloworld!";
	char s2[] = "abcdefghijk";
	char *p = NULL,*q = NULL;
	p = s1;
	q = s2;
	while(*q != '\0')
	{
		*p = *q;
		p++;
		q++;
	}
	*p = *q;
	printf("s1 = %s\n",s1);
	return 0;
}

Homework

Homework ：
1. By pointer strcat function

#include <stdio.h>
#include <string.h>

int main(int argc, char const *argv[])
{
    char s1[32] = "hello world";
    char s2[] = "abcdefg";

    char *p1 = &s1[strlen(s1)];
    char *p2 = s2;

    while(*p2 != '\0')
    {

        *p1 = *p2;
        p1++;
        p2++;
    }
    *p1 = '\0';

    printf("%s\n",s1);


    return 0;
}

2. Realization atoi Function functions
char str[] = '5891";
int num;
…
“5891” ----->5891
3. Enter a string , How many spaces are there in the output string
4. Enter two strings , Determine whether one string is a substring of another
s1 = hellloworld s2 = oworl