#include <stdio.h>
#include <assert.h>
void* my_memcpy(void* dest,const void* src,size_t n)
{
    assert(dest != NULL && src != NULL && n > 0);
    char* dest_t = (char*)dest;
    const char* src_t  = (char*)src;
    while(n--)
        *dest_t++ = *src_t++;
    return dest;
}
int main(void)
{
    char str[] = "abcedf";
    char  buf[20] = "aaaaaaaa";
    my_memcpy(str,buf,sizeof(str));
    printf("%s\n",(char*)str);
    return 0;
}

#include <stdio.h>
void* my_memmove(void* dest,const void* src,size_t n)
{
    char* d = (char*)dest;
    const char* s = (char*)src;
    if( d < s) //start copying  at begining while dest is little
    {
        while(n--)
            *d++ = *s++;
    }
    else if(d > s) //start copying at end while dest is bigger
    {
        d += n - 1;
        s += n - 1;
        while(n--)
            *d-- = *s--;
    }
    return dest;
}

#include <stdio.h>
#include <assert.h>
int my_atoi(char* pstr)
{
    assert(pstr != NULL);
    int res = 0;
    int sign = 1;
    while(*pstr == ' '|| *pstr == '\t')
        pstr++;
    sign = (*pstr == '-'? -1 : 1); /*求得符号位置*/
    if(*pstr == '-' || *pstr == '+') /*跳过符号位置*/
        pstr++;
    while(*pstr != '\0' && *pstr >= '0' && *pstr <= '9')
    {
        res = *pstr - '0' + res*10;
        pstr++;
    }
    return sign*res; /*返回带符号的值*/
}
int main(void)
{
    char a[] = "-110000";
    char b[] = "  456";
    int c = 0;
    c = my_atoi(a);
    printf("%d\n",c);
    c = my_atoi(b);
    printf("%d\n",c);
    return 0;
}