#include<stdio.h>

 #include<assert.h>

 char *mystrcpy(char *dest, const char *src)

 {

     assert((dest != NULL) && (src != NULL));

     char *res = dest;

     while ((*dest++ = *src++) != '\0');

     return res;

 }

 int main()

 {

     char *src = "";

     char dest[];

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

     char *res = mystrcpy(dest, src);

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

     return ;

 }

 #include<stdio.h>

 #include<assert.h>

 char* mystrncpy(char *dest, const char *src, size_t size)

 {

     assert((dest != NULL) && (src != NULL));

     char *res = dest;

     int i = ;

     while (((*dest++ = *src++) != '\0') && (i++<size));

     *(res + size) = '\0';

     return res;

 }

 int main()

 {

     char *src = "";

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

     char dest[];

     char *res = mystrncpy(dest, src, );

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

     return ;

 }

 #include<stdio.h>

 #include<assert.h>

 int mystrlen(const char *str)

 {

     assert(str != NULL);

     int len = ;

     while ((*str++) != '\0')

         ++len;

     return len;

 }

 int main()

 {

     char *str = "";

     int len = mystrlen(str);

     printf("%d\n", len);

     return ;

 }

 #include<stdio.h>

 #include<assert.h>

 int strlenRecur(const char *str)

 {

     if (str == NULL || *str == '\0')

         return ;

     return strlenRecur(str + ) + ;

 }

 int main()

 {

     char *str = "";

     int len = strlenRecur(str);

     printf("%d\n", len);

     return ;

 }

 #include<stdio.h>

 #include<assert.h>

 char* mymemcpy1(char *dest, const char *src, size_t size)

 {

     assert((dest != NULL) && (src != NULL));

     char *res = dest;

     while (size)

     {

         *(dest++) = *(src++);

         --size;

     }

     *(dest + size) = '\0';

     return res;

 }

 int main()

 {

     char *src = "";

     char dest[];

     char *res = mymemcpy1(dest, src,);

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

     return ;

 }

 #include<stdio.h>

 #include<assert.h>

 char *mymemcpy2(char *dest, const char *src, size_t size)

 {

     assert((dest != NULL) && (src != NULL));

     char *res = dest;

     if (dest > src&&dest < (src + size))

     {

         dest = dest + size - ;

         src = src + size - ;

         while (size--)

             *dest-- = *src--;

     }

     else

         while (size--)

             *dest++ = *src++;

     *(dest + size) = '\0';

     return res;

 }

 int main()

 {

     char *src = "";

     char dest[];

     char *res = mymemcpy2(dest, src,);

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

     return ;

 }

 #include<stdio.h>

 #include<assert.h>

 void *mymemset(void *buf, const char c, size_t size)

 {

     assert(buf != NULL);

     char *res = (char*)buf;

     char *str = res;

     while (size--)

         *str++ = c;

     return res;

 }

 int main()

 {

     char *src = "";

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

     char dest[];

     void *buf = (char*)dest;

     char *res = (char *)(mymemset(buf, 'a', ));

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

     return ;

 }

 #include<stdio.h>

 #include<assert.h>

 char *mystrcat(char *dest, const char *src)

 {

     assert((dest != NULL) && (src != NULL));

     char *res=dest;

     while (*dest != '\0')

         ++dest;

     while (*src != '\0')

         *dest++ = *src++;

     return res;

 }

 int main()

 {

     char dest[] = "";

     char *src = "abc";

     char *res = mystrcat(dest, src);

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

     return ;

 }

 #include<stdio.h>

 #include<assert.h>

 char *mystrncat(char *dest, const char *src,size_t size)

 {

     assert((dest != NULL) && (src != NULL));

     char *res=dest;

     while (*dest != '\0')

         ++dest;

     while ((*src != '\0')&&(size--))

         *dest++ = *src++;

     *dest = '\0';

     return res;

 }

 int main()

 {

     char dest[] = "";

     char *src = "abcdef";

     char *res = mystrncat(dest, src,);

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

     return ;

 }

 #include<stdio.h>

 #include<assert.h>

 int mystrcmp(const char *str1, const char *str2)

 {

     assert((str1 != NULL) && (str2 != NULL));

     while (*str1&&*str2 && (*str1++ == *str2++));

     return (*str1 - *str2);

 }

 int main()

 {

     char *str1 = "abcde";

     char *str2 = "abdf";

     int res = mystrcmp(str1, str2);

     printf("%d\n", res);

     return ;

 }

 #include<stdio.h>

 #include<assert.h>

 int mystrncmp(const char *str1, const char *str2,size_t size)

 {

     assert((str1 != NULL) && (str2 != NULL));

     while (*str1&&*str2 && (*str1++ == *str2++)&&size--);

     return (*str1 - *str2);

 }

 int main()

 {

     char *str1 = "abcde";

     char *str2 = "abdfsd";

     int res = mystrncmp(str1, str2,);

     printf("%d\n", res);

     return ;

 }

 #include<stdio.h>

 #include<assert.h>

 char *mystrchr(const char *str, char c)

 {

     assert(str != NULL);

     while (*str != '\0' && (*str != c))

         ++str;

     if (*str == c)

         return (char*)str;

     else

         return NULL;

 }

 int main()

 {

     char *str = "abcde";

     char *res = mystrchr(str,'c');

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

     return ;

 }