C language string summary

Common string operations, list these first.

#include<stdio.h>
#include<string.h>
#include<ctype.h>
// delete the specified character from the string
char * DeleteChar(char *s, char c)//c is the character to be deleted
{
	int i, j = 0;
	for ( i = 0; *(s + i) != '\0'; i++)
	{
		if (*(s + i) != c)
		{
			*(s + j) = *(s + i);
			j++;
		}
	}
	*(s + j) = '\0';
	return s;
}

// find the length of the string
int str_length(const char *s)
{
	int count = 0;
	while (*s++ != '\0')
	{
		count++;
	}
	return count;
}


// string case conversion
void Tolower(char *s)
{
	
	for (int i = 0; *(s + i) != '\0'; i++)
	{
		if (*(s + i) >= 65 && *(s + i) <= 90)
		{
			*(s + i) = *(s + i) + 32;
		}
	}
		
}

//string concatenation
char * str_cat(char *s1, const char *s2)
{
	char *temp = s1;
	while (*s1 != '\0')
	{
		s1 ++;
	};
	while (*s2 != '\0')
	{
		* s1 ++ = * s2 ++;
	}
	* s1 = '\ 0';
	return temp;

}


// string copy		
char * str_cpy(char *s1, char *s2)
{
	char *temp = s1;
	while (*s2 != '\0')
	{
		* s1 ++ = * s2 ++;
	}
	* s1 = '\ 0';
	return temp;
}


int main(void)
{
	char s[20] = "hefahifAZfpiwf";

	//string length
	printf("The length of the string is %d\n", str_length(s));

	//remove the 'h' character from the string
	DeleteChar(s, 'h');
	printf("%s\n", s);

	//Convert to lowercase characters
	Tolower(s);
	printf("Convert to lowercase: %s\n", s);

	// concatenate two characters
	char s1[30] = "haha";
	char s2[10] = "ffafhi";
	str_cat(s1, s2);
	printf("After connecting s2 to s1: %s\n", s1);

	char s3[10] = "zhaf";
	char s4[10] = "fah";
	str_cpy (s3, s4);
	printf("After copying s4 to s3: %s\n", s3);
}

C language comes with string processing functions

1.strlen, find the length of the string

size_t strlen(const char *s)
{
	size_t len = 0;
	while (*s++)
		len ++;
	return len;
}

String length excluding null characters

2.strcpy, string copy

char *strcpy(char *s1, const char *s2)
{
	char *temp = s1;
	while (*s1++ = *s2++);
	return temp;
}