This problem is basis on one string is user input, another is defined by two object and this two other concatenation by another object is done by this program

String Concat

#include <iostream>
#include <cstring>
using namespace std;
static const int string1=1;
static const int string2=2;
static const int string3=3;
class str
{

public :

int l;
char mystr[40];
char mystr1[40];
str()
{
l=0;
cout<<"Pls enter your first string : "<<endl;
cin.getline(mystr,40);

}
str(char *s)
{
l=strlen(s);
strcpy(mystr1,s);

}

void concat(str r, str t);

};
void str::concat(str r, str t)
{

strcat(r.mystr," ");
strcat(r.mystr,t.mystr1);
cout<<endl<<endl<<r.mystr<<endl<<endl;
}
int show(str p,str q)
{
int index;

while(true)
{
cout<<endl<<endl<<"1 for string 1"<<endl<<"2 for string 2"<<endl;
cout<<"3 for string concatenation"<<endl;
cout<<"4 for exit the programe."<<endl;
cout<<"What do you want : ";
cin>>index;
switch(index)
{
case string1:
cout<<endl<<endl<<p.mystr<<endl<<endl;
break;

case string2:
cout<<endl<<endl<<q.mystr1<<endl<<endl;
break;

case string3:
p.concat(p,q);
break;

default :
cout<<endl<<endl<<"Thanks for your operation"<<endl;
return 0;
}
}
}
int main()
{
str o,o1("Hello world");
show(o,o1);
return 0;
}