#include <iostream>
using namespace std;
typedef struct{
    char *ch;
    int length;
}HString;
bool StrAssign(HString &T,char *chars);
int StrLength(HString S);
int StrCompare(HString S,HString T);
bool ClearString(HString &S);
bool Concat(HString &T,HString S1,HString S2);
HString SubString(HString S,int pos,int len);
bool StrInsert(HString &S,int pos,HString T);
void StrTraverse(HString S);
bool StrAssign(HString &T,char *chars)
{
    int i;
    char *c=chars;
    if(T.ch)free(T.ch);
    for(i=0;c;i++,++c);
    if(!i){T.ch=NULL;T.length=0;}
    else{
        if(!(T.ch=(char *)malloc(i*sizeof(char))))
            exit(0);
        for(int j=0;j<i;j++)
            T.ch[i]=chars[i];
        T.length=i;
    }
    return true;
}
int StrLength(HString S)
{
    return S.length;
}
int StrCompare(HString S,HString T)
{
    for(int i=0;i<S.length&&i<T.length;i++)
        if(S.ch[i]!=T.ch[i])return S.ch[i]-T.ch[i];
    return S.length-T.length;
}
bool ClearString(HString &S)
{
    if(S.ch){free(S.ch);S.ch=NULL;}
    S.length=0;
    return true;
}
bool Concat(HString &T,HString S1,HString S2)
{
    if(T.ch)free(T.ch);
    if(!(T.ch=(char *)malloc((S1.length+S2.length)*sizeof(char))))
        exit(0);
    for(int i=0;i<S1.length;i++)
        T.ch[i]=S1.ch[i];
    T.length=S1.length+S2.length;
    for(int i=S1.length;i<T.length;i++)
        T.ch[i]=S2.ch[i-S1.length];
    return true;
}
bool SubString(HString &Sub,HString S,int pos,int len)
{
    if(pos<1||pos>S.length||len<0||len>S.length-pos+1)
        return false;
    if(Sub.ch)free(Sub.ch);
    if(!len){Sub.ch=NULL;Sub.length=0;}
    else{
        Sub.ch=(char *)malloc(len*sizeof(char));
        for(int i=0;i<len;i++)
            Sub.ch[i]=S.ch[i+pos-1];
        Sub.length=len;
    }
    return true;
}
bool StrInsert(HString &S,int pos,HString T)
{
    if(pos<1||pos>S.length)return false;
    if(T.length){
        if(!(S.ch=(char *)realloc(S.ch,(S.length+T.length)*sizeof(char))))
            exit(0);
        for(int i=S.length-1;i>=pos-1;i--)
            S.ch[i+S.length]=S.ch[i];
        for(int i=pos-1;i<pos+T.length-1;i++)
            S.ch[i]=T.ch[i-pos+1];
    }
    return true;
}
void StrTraverse(HString S)
{
    if(S.length){
        for(int i=0;i<S.length;i++)
            cout<<S.ch[i];
    }
    cout<<endl;
}
int main()
{
    HString S1,S2,T,S,Sub;
    StrAssign(S1,"welcome to computer");
    StrAssign(S2,"I like Date Structers!");
    StrAssign(T,"C++");
    cout<<"S1:";
    StrTraverse(S1);
    cout<<"the length is "<<StrLength(S1)<<endl;
    cout<<"S2:";
    StrTraverse(S2);
    cout<<"the length is "<<StrLength(S2)<<endl;
    cout<<"T:";
    StrTraverse(T);
    cout<<"the length is "<<StrLength(T)<<endl;
    if(StrCompare(S1,S2)>0)cout<<"S1>S2";
    else
        if(StrCompare(S1,S2)<0)cout<<"S1<S2";
    else
        cout<<"S1=S2";
    cout<<endl;
    Concat(S,S1,S2);
    cout<<"S:";
    StrTraverse(S);
    StrInsert(S1,6,T);
    cout<<"new S1:";
    StrTraverse(S1);
    SubString(Sub,S2,3,5);
    cout<<"Sub:";
    StrTraverse(Sub);
    return 0;
}