Mathematical design D12 according to string function

One . The string src copy to des in

Law 1

void Mystrcpy(char*des,char*src)
{
	int i;
	for(i=0;src[i]!='\0';i++)//'\0' At the end of the string token 
	{
		des[i]=src[i];
	}
	des[i]='\0'; 
 } 

Law 2

char *p=arr;// The array name indicates the address of the first element of the array

Arrays and pointers have the following equations ：p[i]==*(p+i);     arr[i]==*(arr+i)

void Mystrcpy 1(char*des,char*src)
{
	int i;
	for(i=0;*(src+i)!='\0';i++)
	{
		*(des+i)=*(src+i);
	}
	*(des+i)='\0'; 
 } 

Law 3

void Mystrcpy 2(char*des,char*src)
{
	for(char*p=src;*p!='\0';p++)
	{
		printf("%c",*p);
	}
	while(*src!='\0')
	{
		*des=*src;
		src++;
		des++;
	}
	*des='\0';
}

Law 4

++ and * Same order operation , The operation order is from right to left

void Mystrcpy 2(char*des,char*src)
{
	while(*des++=*src++);

}

Two . Find the string length

1. Find the string length directly

#include<string.h>// quote 
printf("%d\n",strlen(str));// Output usage 

2. Find string str The length of "abcd" by 4, barring '\0', Only the valid length of the string is returned

int Mystrlen(char*str)
{
	int i;
	for(i=0;str[i]!='\0';i++)
	{
	}
	return i;
}

p[i]=*(p+i)

arr[i]=*(arr+i) These can be substituted with the above