C++字符串操作二

#include <iostream>
#include <assert.h>
using namespace std;
//模拟实现strcmp函数。
bool my_strcmp(const char *str1,const char *str2)
{
    assert(str1!=NULL && str2!=NULL);
    const char *p = str1;
    const char *q = str2;
    while (*p != ‘\0‘ && *q != ‘\0‘ && *p == *q)
    {
        p++;
        q++;
    }
    return (*p - *q)!=0;
}
int main()
{
    cout << my_strcmp("liwu", "liu") << endl;
    return 0;
}




#include <iostream>
#include <assert.h>
using namespace std;
//库函数memcopy的实现。
char *my_memcopy(char *dist, const char *src, int len)
{
    assert(dist != NULL && src != NULL);
    char *p = dist;
    int n = len>(strlen(src)+1) ? strlen(src)+1 : len;
    while (n-->0)
    {
        *dist++ = *src++;
    }
    return p;
}
int main()
{
    char s1[20] = "1234";
    my_memcopy(s1,"liuhuiyan",2);
    cout << s1 << endl;
}

#include <iostream>
#include <assert.h>
using namespace std;
char* my_memove(char *dist,const char* src,int len)
{
    assert(dist!=NULL && src!=NULL);
    char *p = dist;
    const char *q = src;

    int n = len>(strlen(src) + 1) ? strlen(src) + 1 : len;
    if (p <= q || q+n<=p)
    {
        while (n-- > 0)
        {
            *p++ = *q++;
        }
    }
    else
    {
        p += n-1;
        q += n-1;
        while (n-- > 0)
        {
            *p-- = *q--;
        }
    }
    return dist;
}
int main()
{
    char s1[] = "liu hui yan";
    char s2[] = "123 456";
    cout << my_memove(s1, s2, 6) << endl;
    return 0;
}


#include <iostream>
using namespace std;
//一个字符串“student a am i”，现要求将这个字符串修改为“i am a student”。
void exchange(char *p1,char *p2)
{
    char temp;
    while (p1 < p2)
    {
        temp = *p1;
        *p1 = *p2;
        *p2 = temp;
        p1++;
        p2--;
    }
}
char* my_exchange(char *src)
{
    char *p = src;
    char *q = src;
    while (*p != ‘\0‘)
    {
        while (*p != ‘ ‘ && *p!=‘\0‘)
        {
            p++;
        }
        exchange(q,p-1);
        if (*p == ‘\0‘)break;
        p++;
        q = p;
    }
    exchange(src,p-1);
    return src;
}
int main()
{
    char s[] = "student a am i";
    cout << my_exchange(s) << endl;
}


//字符串打印数字。
#include <iostream>
#include <assert.h>
using namespace std;
int my_int(const char *str)
{
    assert(str!=NULL);
    int count = 0;
    while (*str != ‘\0‘)
    {
        count = (count * 10 + *str - ‘0‘);
        str++;
    }
    return count;
}
int main()
{
    char s[] = "12345";
    cout << my_int(s) << endl;
    return 0;
}

#include <iostream>
using namespace std;
char str[] = { ‘0‘, ‘1‘, ‘2‘, ‘3‘, ‘4‘, ‘5‘, ‘6‘, ‘7‘, ‘8‘, ‘9‘ };
//输入数字1234，打印相应的字符串。
void Printf(int x)
{

    if (x==0)return;
    else
    {
        Printf(x / 10);
        cout << str[x % 10] << endl;
    }

}
int main()
{
    Printf(1234);
    return 0;
}