C++ reversing a string with only one string - c++

Question

I am trying to reversing a string with only using one string, but when I output the string it is missing a letter. Is something being over written that I do not know about? Here is my code:
#include <iostream>
using namespace std;
int main() {
string d = "jakejosh"; //11
char temp = '\0';
int j = d.size()/2;
for (int i=d.size()/2; i> 0; i--) //5
{
temp = d[i+j];
d[j+i] = d[j-i];
d[j-i] = temp;
}
cout << d << endl;
return 0;
}
Output is: ttam olle
Output should be: ttam olleh

Answer 1

When the size of a string is even then the code is wrong. For example if the size is equal to 2 then size() / 2 is equal to 1 and in the loop you will get thet d[i+j] is equivalent to d[size() / 2 + size() / 2] that is equal to d[2] while the valid range of indices is [0,1]
Also you should include header <string> and you could use standard function std::swap
The simplest approach is the following
#include <iostream>
#include <string>
int main()
{
std::string s = "hello matt";
s = std::string( s.rbegin(), s.rend() );
std::cout << s << std::endl;
return 0;
}
If you want to write the loop yourself then the code can look like
#include <iostream>
#include <string>
int main()
{
std::string s = "hello matt";
for ( std::string::size_type i = 0; i < s.size() / 2; i++ )
{
char c = s[i];
s[i] = s[s.size()-i-1];
s[s.size()-i-1] = s[i];
}
std::cout << s << std::endl;
return 0;
}
Or you can write some exotic solution.:) For example
#include <iostream>
#include <string>
#include <utility>
int main()
{
std:: string s = "Jake Smith";
std::cout << s << std::endl;
for ( std::string::size_type i = 0, j = s.size(); j - i > 1; i++ )
{
std::swap( s[i], s[--j] );
}
std::cout << s << std::endl;
return 0;
}
The program output is
Jake Smith
htimS ekaJ
Or you can try to write a recursive function.
At last you could use standard algorithm std::reverse declared in header <algorithm>.

Answer 2

Use std::reverse() to do that. For educational purposes take a look at the following pure C algorithms: http://www.programmingsimplified.com/c-program-reverse-string

Answer 3

for (int i=d.size()/2; i> 0; i--) //5
{
temp = d[i+j-1]; // d[9] i.e.must be 9 not 10 for swapping with 'h'
d[j+i-1] = d[j-i];
d[j-i] = temp;
}

Answer 4

It's very easy to trip up with indices when reversing a string in place.
If your string is of length LEN, then the valid indices are 0 - N-1.
In your case, let's take a look at the middle and how you start swapping from there.
hello matt
For reversing the string, you'll have to swap
hello matt (swap 0-th and 9-th)
^ ^
hello matt (swap 1-st and 8-th)
^ ^
hello matt (swap 2-nd and 7-th)
^ ^
hello matt (swap 3-rd and 6-th)
^ ^
hello matt (swap 4-th and 5-th)
^^
The start value for i is (N-1)/2.
The end vale for i is 0.
The index for swapping the value at i is len - 1 - i. (swap d[0] with d[9] in your case)
Putting that all together, the function should be something like:
void reverse_string(string& d)
{
int len = d.length();
for (int i=(len-1)/2; i >= 0; i--)
{
int j = len - 1 - i;
char temp = d[j];
d[j] = d[i];
d[i] = temp;
}
}
Here's the main function to test it.
int main()
{
string d = "hello matt";
reverse_string(d);
cout << d << endl;
d = "hello max";
reverse_string(d);
cout << d << endl;
return 0;
}