数据结构，串操作出现乱码

问题遇到的现象和发生背景

问题相关代码，请勿粘贴截图

运行结果及报错内容

我的解答思路和尝试过的方法

我想要达到的结果

#include<iostream>
using namespace std;

typedef struct {
    /* data */
    char *ch;
    int length;
}Str, *str;

int strassign(Str& str, char* ch);   //调用格式srassign(str, "cur input")
int strlength(Str str);
int strcompare(Str s1, Str s2);
int concat(Str& str, Str str1, Str str2);
int substring(Str& substr, Str str, int pos, int len);
int clearstring(Str& str);
void strdispiay(Str str);

int main(){
    
    str a = new Str;   
    str b = new Str;
    str c = new Str;

    strassign(*a, "HelloWorld");
    strdispiay(*a);
    cout << "a串的长度为：" << strlength(*a) << endl;

    strassign(*b, "world!");
    strdispiay(*b);
    cout << "b串的长度为：" << strlength(*b) << endl;
    //cout << strassign(b, "hello") << endl;

    switch(strcompare(*a, *b) == 0? 0 : (strcompare(*a, *b) < 0? -1 : 1)){
        case -1:
            cout << "串b大" << endl;
        case 0:
            cout << "相等" << endl;
        case 1:
            cout << "串a大" << endl;
    }

    concat(*c, *a, *b);
    strdispiay(*c);
    cout << "c串的长度为：" << strlength(*c) << endl;


    system("pause");
    return 0;
}

int strassign(Str& str, char* ch){
    if(str.ch)
        delete(&str.ch);
    int len = 0;
    char *c = ch;
    while (*c){
        /* code */
        ++len;
        ++c;
    }
    if(len == 0){
        str.ch = NULL;
        str.length = 0;
        return 1;
    }
    else{
        str.ch = new char[len +1];
        if(str.ch == NULL)
            return 0;
        else{
            c = ch;
            for(int i = 0; i <= len; ++i, ++c)
                str.ch[i] = *c;
            str.length = len;
            return 1;
        }
    }
}

int strlength(Str str){
    return str.length;
}

int strcompare(Str s1, Str s2){
    for(int i = 0; i < s1.length && i < s2.length; ++i)
        if(s1.ch[i] != s2.ch[i])
            return s1.ch[i] - s2.ch[i];
    return s1.length - s2.length;
}

int concat(Str& str, Str str1, Str str2){
    if(str.ch){
        delete(&str.ch);
        str.ch = NULL;
    }
    str.ch = new char[str1.length + str2.length + 1];
    if(str.ch == NULL)
        return 0;
    int i = 0;
    while(i < str1.length){
        str.ch[i] = str1.ch[i];
        ++i;
    }
    int j = 0;
    while(j <= str2.length){
        str.ch[i+j] = str2.ch[j];
        ++j;
    }
    str.length = str1.length + str2.length;
    return 1;
}

int substring(Str& substr, Str str, int pos, int len){
    if(pos < 0 || pos >= str.length || len < 0 || len > str.length - pos)
        return 0;
    if(substr.ch){
        delete(&substr.ch);
        substr.ch = NULL;
    }
    if(len == 0){
        substr.ch = NULL;
        substr.length = 0;
        return 1;
    }
    else{
        substr.ch = new char[len+1];
        int i = pos;
        int j = 0;
        while(i < pos+len){
            substr.ch[j] = str.ch[i];
            ++i;
            ++j;
        }
        substr.ch[j] = '\0';
        substr.length = len;
        return 1;
    }
}

int clearstring(Str& str){
    if(str.ch){
        delete(&str.ch);
        str.ch = NULL;
    }
    str.length = 0;
    return 1;
}

void strdispiay(Str str){
    for(int i = 0; i < str.length; i++)
        cout << str.ch[i];
    cout << endl;
}