C language: some self realization of string functions

Catalog

One 、 String function

1. Realize my strlen（）

2. My string copy

3. String splicing

4. String comparison

Two 、 String practice

1. Find the first subscript of a character in another string

 2. Return to the first address

3. Find the address where one string appears in another string abcccccde ccd

4. Count the number of words in the string

5. Insert one string into another

6. Flip strings

7.GetString（）

---

One 、 String function

1. Realize my strlen（）

#include <stdio.h>

int MyStrlen(char* str)
{
	int count = 0;
	while (*str != '\0')
	{
		count++;
		str++;
	}
	str = '\0';
	return count;
}
int main()
{

	char str[] = "abcde";
	printf("%d\n", MyStrlen(str));


	return 0;
}

2. My string copy

#include <stdio.h>


char* MyStrcpy(char* str1, char* str2)
{
	char* pMark = str1;
	while (*str2 != '\0')
	{
		*str1 = *str2;
		str1++;
		str2++;
	}
	*str1 = '\0';
	return pMark;
}
int main()
{
	char str[20];
	char str1[] = "abcde";

	printf("%s\n", MyStrcpy(str, str1));

	return 0;
}

3. String splicing

#include <stdio.h>

char* MyStrCat(char* str1, char* str2)
{
	char* pMark = str1;
	while (*str1 != '\0')
	{
		str1++;
	}
	while (*str2 != '\0')
	{
		*str1 = *str2;
		str1++;
		str2++;
	}
	*str1 = '\0';
	return pMark;
}
int main()
{
	char str[10] = "abcd";
	char* str1 = "1234";
	printf("%s\n", MyStrCat(str,str1));

	return 0;
}

4. String comparison

#include <stdio.h>

int MyStrcmp(char* str1,char* str2)
{
	/*while (*str1 != '\0' && *str2 != '\0')  // The first method 
	{
		if (*str1 > *str2)
		{
			return 1;
		}
		else if (*str1 < *str2)
		{
			return -1;
		}
		else
		{
			str1++;
			str2++;
		}
	}
	if (*str1 > *str2)
	{
		return 1;
	}
	else if (*str1 < *str2)
	{
		return -1;
	}
	else
	{
		return 0;
	}*/
	while (*str1 != '\0' || *str2 != '\0')   // The second method 
	{
		if (*str1 > *str2)
		{
			return 1;
		}
		else if (*str1 < *str2)
		{
			return -1;
		}
		else
		{
			str1++;
			str2++;
		}
	}
	return 0;
}
int main()
{

	printf("%d\n", MyStrcmp("abc", "abc"));
	printf("%d\n", MyStrcmp("ab", "abc"));
	printf("%d\n", MyStrcmp("ac", "abc"));




	return 0;
}

Two 、 String practice

1. Find the first subscript of a character in another string

#include <stdio.h>
int T1(char* str, char ch)
{
	int count = 0;
	while (*str != '\0')
	{
		if (*str == ch)
		{
			return count;
		}
		str++;
		count++;
	}
	return  -1;
}
int main()
{
	printf("%d\n", T1("abcd", 'b'));
	return 0;
}

  Output ：

1      // Because it is the following table, it is the second element 

D:\c++\c Language \ character string \x64\Debug\ character string .exe ( process  4356) Exited , The code is  0.
 To automatically close the console when debugging stops , Please enable “ Tools ”->“ Options ”->“ debugging ”->“ Automatically close the console when debugging stops ”.
 Press any key to close this window . . .

 2. Return to the first address

#include <stdio.h>
char* T2(char* str, char ch)
{
	while (*str != '\0')
	{
		if (*str == ch)
		{
			return str;
		}
		str++;
	}
	return NULL;
}
int main()
{
	printf("%c\n",*T2("abcd",'b'));
	return 0;
}

Output

b     // Because you want to be easy to observe   So use %c Print 

D:\c++\c Language \ character string \x64\Debug\ character string .exe ( process  17304) Exited , The code is  0.
 To automatically close the console when debugging stops , Please enable “ Tools ”->“ Options ”->“ debugging ”->“ Automatically close the console when debugging stops ”.
 Press any key to close this window . . .

3. Find the address where one string appears in another string abcccccde ccd

#include <stdio.h>
#include <stdlib.h>
char* t3(char* str1, char* str2)
{
	while (*str1 != '\0')
	{
		if (0 == strncmp(str1, str2, strlen(str2)))
		{
			return str1;
		}
		str1++;
	}
	return NULL;
 }
int main()
{
	printf("%s\n", t3("abcccccde", "ccd"));
	return 0;
}

Output

ccde               // For convenience of observation , So use %c Print 

D:\c++\c Language \ character string \x64\Debug\ character string .exe ( process  22856) Exited , The code is  0.
 To automatically close the console when debugging stops , Please enable “ Tools ”->“ Options ”->“ debugging ”->“ Automatically close the console when debugging stops ”.
 Press any key to close this window . . .

4. Count the number of words in the string

#include <stdio.h>
int T4(char* str)
{
	int count = 0;
	while (*str != '\0')
	{
		if (*str == ' ')
		{
			count++;
		}
		str++;
	}
	return count + 1;
}
int main()
{
	printf("%d\n", T4("i love you"));
	return 0;
}

Output

3
 
D:\c++\c Language \ character string \x64\Debug\ character string .exe ( process  19016) Exited , The code is  0.
 To automatically close the console when debugging stops , Please enable “ Tools ”->“ Options ”->“ debugging ”->“ Automatically close the console when debugging stops ”.
 Press any key to close this window . . .

5. Insert one string into another

#include <stdio.h>
void T5(char* str1, char* str2, int n)
{
	char* phead = str1 + n - 1;
	char* pend = str1 + strlen(str2);
	while(phead <= pend)
	{
		*(pend + strlen(str2)) = *pend;
		pend--;
	}
	while (*str2 != '\0')
	{
		*phead = *str2;
		phead++;
		str2++;
	} 
}
int main()
{
	char str[20] = "abcd";
	T5(str, "12345", 3);
	printf("%s\n", str);
	return 0;
}

  Output

ab12345cd

D:\c++\c Language \ character string \x64\Debug\ character string .exe ( process  14688) Exited , The code is  0.
 To automatically close the console when debugging stops , Please enable “ Tools ”->“ Options ”->“ debugging ”->“ Automatically close the console when debugging stops ”.
 Press any key to close this window . . .

6. Flip strings

#include <stdio.h>
void T6(char* str)
{
	char* pbegin = str;
	char* pend = str + strlen(str) - 1;
	while (pbegin < pend)
	{
		char ptemp = *pbegin;
		*pbegin = *pend;
		*pend = ptemp;
		pbegin++;
		pend--;
	}
}
int main()
{
	char str[20] = "abcd";
	T6(str);
	printf("%s\n", str);

	return 0;
}

  Output

dcba

D:\c++\c Language \ character string \x64\Debug\ character string .exe ( process  9832) Exited , The code is  0.
 To automatically close the console when debugging stops , Please enable “ Tools ”->“ Options ”->“ debugging ”->“ Automatically close the console when debugging stops ”.
 Press any key to close this window . . .

7.GetString（）

#include <stdio.h>
#include <stdlib.h>
char* Getstring()
{
	int size = 5;
	char* str = (char*)malloc(sizeof(char) * size);
	int count = 0;
	char ch;

	while ((ch = getchar()) != '\n')
	{
		str[count] = ch;
		count++;
		if (count == size)
		{
			size += 5;
			str = realloc(str, size);
		}
	}
	str[count] = '\0';
	return str;
}
int  main()
{
	char* str = Getstring();
	printf("%s\n", str);
	free(str);
	return 0;
}

Output

1234
1234

D:\c++\c Language \ character string \x64\Debug\ character string .exe ( process  18236) Exited , The code is  0.
 To automatically close the console when debugging stops , Please enable “ Tools ”->“ Options ”->“ debugging ”->“ Automatically close the console when debugging stops ”.
 Press any key to close this window . . .