Reversing Strings

Hello Again,

Does anyone have a piece of code that can flip a string around or know how an easy way to do this? I am working on a special calculator that has will compute a variation of two's compliment. I am not good at all with string manipulation.

An example of this would be:

INPUT: halo
OUTPUT: olah

Thank You!

Try the reverse standard algorithm:

Code:

---

# include <string>
# include <algorithm>
# include <iostream>

using namespace std;

int main()
{
        string s = "halo";

        cout << "String is: " << s << endl;

        std::reverse<string::pointer>(s.begin(), s.end());

        cout << "Reverse string is: " << s << endl;
        return 0;
}

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You can do it this way too:

Code:

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string str = "halo";
string reversed;

for(int i = str.length() - 1; i >= 0; i--)
{
        reversed += str[i];
}
cout<<reversed<<endl;

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I know this is an old topic, but why create a new topic when this is exactly what I need.

Ok, can you comment (//) on the piece of coding 7stud wrote^^. Im trying to understand this but how does the computer know to place character X into the Y position.

thnx!!!

You're not supposed to post in threads over 2 weeks old. :)

7stud's code just takes the last character of str and adds it to reversed, making it the first character. Then it takes the next-to-last character and adds it to the end of reversed, which makes it the second character. And so on until the beginning of the string.

if you are using char[] arrays, you can simply swap the elements

a slightly more efficient method is to also use a reverse-iterator, which starts at the end of the new string and the beginning of the old string.

In each iteration, the following happens:

• The first character of the source string is written to the last character of the target string
• The last character of the source string is written to the first character of the target string
• The forward iterator is increased by one
• The reverse iterator is decreased by one

I can see how this could be confusing to read, so here's a bit of code to show you more:

Code:

---

#include <iostream>        //for standard console I/O
#include <cstring>        //for strlen()

int main()
{
        char source[]="dlroW olleH";        //the source string
        char target[]="dlroW olleH";        //the target string
        register short int f;                //the forward iterator
        register short int r;                //the reverse iterator

        /*
        * this line gets the length of the source string.  In this case, I
        * made sure both strings were the same length.  You could, after this
        * point, allocate a target string just for the purposes of copying.
        */
        register const short int LEN=strlen(source);

        /*
        * This is the "magic loop".  What it does is set sthe forward iterator
        * to zero, the reverse iterator to the last index to be copied, and
        * loops until they are of equal size (or somehow they pass eachother).
        * In each iteration, it increases the forward iterator and decreases
        * the reverse iterator.  The iterators work their ways from the ends
        * of the string to the center.
        */
        for(f=0,r=LEN-1; f<r; f++,r--)
        {
                /*
                * The first line copies the first character in source to be
                * copied into the last character in target to be written.
                * The second line does the same, except it uses the last char
                * in source to be read to write into the first position of
                * target to be written.
                */
                target[r]=source[f];
                target[f]=source[r];
        }

        std::cout<<target<<std::endl;        //output the target string
        return 0;                        //be nice to your creator.
}

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