Reversing Strings

[Halo]

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!

[IfYouSaySo]

Try the reverse standard algorithm:

# 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;
}

[7stud]

You can do it this way too:

string str = "halo";
string reversed;

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

[stevedawg85]

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!!!

[dwks]

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.

[jlf029]

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

[major_small]

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:

#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.
}