How to reverse a string in pairs?

[myrongainz]

I'm trying to reverse a string in pairs
Example: input - heaven
output - ne va eh
My code seems to be right until the last for loop...
That's where I need help
Here's my code:

#include <iostream>
#include <string>
using namespace std;
string revString(string user);
int main()
{
    string user;
    cout<<"Enter a random text"<<endl;
    getline(cin,user);
    unsigned int length=user.length();
    while (length%2 == 1)
    {
        cout<<"enter the text with even amount of letters"<<endl;
        getline(cin,user);
        length = user.length();
    }

        string revstr = revString(user);
        cout<<revstr;


       return 0;
}
string revString(string user)
{
    string rev;
    for(int i =1; i<=(int)user.length();i+=2)
    {
        rev = user.length[i+1];
        rev = user.length[i];
    }
    return rev;
}

[vidit_X]

Your code compiles fine? Because length is a function and you are trying to use it as an array

user.length[i]

[myrongainz]

Your code compiles fine? Because length is a function and you are trying to use it as an array

user.length[i]

|29|error: invalid types '<unresolved overloaded function type>[int]' for array subscript|
|30|error: invalid types '<unresolved overloaded function type>[int]' for array subscript|
||=== Build finished: 2 errors, 0 warnings ===|

for the last 2 reverse lines
this 2 lines:
rev = user.length[i+1];
rev = user.length;

[vidit_X]

That is because length is a function, not an array. You cannot have an index for a function. I think you are trying to get the character at that index, for that you can directly use [] with a string.

user[i];

And your logic is flawed, when you'll run the program you'll figure it out.

[stereomatching]

better prefer pass by reference rather than pass by value
there are several easier ways to do this

std::copy(user.rbegin(), user.rend(), std::back_insert(rev) );

or

std::reverse_copy(forward_.begin(), forward_.end(), std::back_inserter(backward_) );

or

std::string forward = "abcdefg"
std::string backward(forward.rbegin(), forward.rend() );

I would prefer the last way, it is easier to understand(for me) and should be more effective

It is not a bad idea to do some practice by hand crafted codes
But prefer the standard algorithms or the function provided by the
containers would be better in most of the cases.

[stereomatching]

forgot one thing
if you only want to reverse the string
you don't need another string
just use

std::reverse(user.begin(), user.end() );

if you need hand crafted codes, try this

void reverse_test( std::string::iterator first, std::string::iterator last)
{
  while ((first!=last)&&(first!=--last))
  {
    std::swap(*first,*last);
    ++first;
  }
}