为什么这个程序显示交换的两个字符串始终有错误？

问题：输入0后，显示的交换的两个字符串不对。

#include <iostream>
#include <cstring>
#define MAX 20

using namespace std;

template <class Anytype>
void exchange(Anytype &a , Anytype &b);

template <class T>
void exchange(T a[], T b[]);

template <typename T>
void display(T a, T b);



int main(){
    int i = 0;
    cin >> i;
    
    if(i != 0){
        cout << "Please enter two fractions\n"; 
    
        double test1 = 0 , test2 = 0;
        cin >> test1 >> test2;
        exchange(test1,test2);
        display(test1,test2);
    }else{
        cout << "please enter two strings\n";
        
        char a[MAX]{'\0'},b[MAX]{'\0'} ;
        cin.getline(a,MAX);
        cin.get();
        cin.getline(b,MAX);
        cin.get();
        
        exchange(a,b);
        display(a,b);
    }
    
    cin.get();
    
    return 0;
} 

template <class T>
void exchange(T &a , T &b){
    T temp;
    temp = a;
    a = b;
    b = temp;
}

template <class T>
void exchange(T a[], T b[]){
    for(int i = 0; i < strlen(a)|| i < strlen(b); i++){
        auto temp = a[i];
        a[i] = b[i];
        b[i] = temp;
    }
}


template <typename T>
void display(T a, T b){
    cout << "a = " << a <<endl;
    cout << "b = " << b <<endl;
}



![img](https://img-mid.csdnimg.cn/release/static/image/mid/ask/370912356736185.png "#left")

已经将第二个函数模版用指针的方式进行修改无效。
不知道是哪里错了

直接cin>>a;
cin>>b;