MyStrlen, MyStrcmp, MyReverse,MyStrcpy,MyStrncpy,Merge,Change

#include <iostream>
#include <cstring>
#include <cassert>
using namespace std;

int MyStrlen(char* a)  //strlen(a)
{
    int i=0;
    while(a[i]!='\0')
    {
        i++;
    }
    return i;
}

int MyStrcmp(char* s, char* t)
{
    assert(s!=NULL);
    assert(t!=NULL);


    while(*s && *t && (*s==*t))
    {
        s++;
        t++;
    }
    if(*s>*t)
    {
        return 1;
    }
    else if(*s<*t)
    {
        return -1;
    }
    else
    {
        return 0;
    }
}

void MyReverse(char* a)  //头尾交换
{
    int size= MyStrlen(a);  // strlen(a);
    for(int i=0; i<size/2; i++)
    {
        char temp=a[i];
        a[i]=a[size-1-i];
        a[size-1-i]=temp;
    }
}

char* MyStrcpy(char* dest, char* src)
{
    assert(dest!=NULL);
    assert(src!=NULL);
    int i=0;
    for(; src[i]!='\0'; i++)
    {
        dest[i]=src[i];
    }
    dest[i]='\000';


    return dest;
}

char* MyStrncpy(char*dest, char* src, int pos)
{
    assert(dest!=NULL);
    assert(src!=NULL);


    int SizeSrc=MyStrlen(src);
    if(SizeSrc>=pos)
    {
        int i=0;
        for(; i<pos; i++)
        {
            dest[i] =src[i];
        }
        return dest;
    }
    else
    {
        int i=0;
        for(;i<SizeSrc; i++)
        {
            dest[i]=src[i];
        }
        //dest[i]='\0';
        return dest;
    }
}

char* Merge(char* dest, char* src)//strcat
{
    int i=0;
    int j=0;
    while(dest[i] !='\0')
    {
        i++;
    }


    while(src[j] !='\0')
    {
        dest[i] = src[j];
        i++;
        j++;
    }
    dest[i]='\0';
    return dest;
}

char* Change(char* a, int pos) // 指定位置前后对换位  pos=3 abc defg -> defg abc
{
    char* temp=new char[pos+1];


    MyStrncpy(temp, a, pos);
    temp[pos]='\0';


    MyStrncpy(a,a+pos,7-pos);


    MyStrncpy(a+7-pos,temp,pos);


    delete [] temp;
    return a;
}

int main()
{
    char a[]="abcdefg";
    cout<<"size of the char a[]: ";
    cout<<MyStrlen(a)<<endl;
    cout<<"Initial char a[]: ";
    cout<<a<<endl;

    MyReverse(a);
    cout<<"after reverse char a[]: ";
    cout<<a<<endl;

    cout<<"after shabi   dadong: ";
    cout<<Change(a,4)<<endl;

    return 0;
}