Hi there,

New to C++ and trying to write a short program to reverse the characters in a word. Im having trouble converting the string to a char array. Here is the code:

#include "stdafx.h"
#include <iostream>
#include <string>
#include <cstring>

using namespace std;

int main()
{
	string org;
	string end;
	cin >> org;

	int num = org.size();

	char reversal[num];
	strcpy(reversal, org.c_str());

	for (int a = num; a >= 0; a--)
	{
		cout << reversal[a];
	}
	cout << endl;
	return 0;
}

Im getting three errors. All are on the strcopy() line:

error C2057: expected constant expression
error C2466: cannot allocate an array of constant size 0
error C2133: 'reversal' : unknown size

Im using Visual C++ to compile.

Any advice you can give is much appreciated and if there is a more efficient way of doing this please let me know. Thanks again!

Pete.

for(std::string::reverse_iterator rit = org.rbegin(); rit !=  org.rend(); ++rit) {
  end += *rit;
}

This uses the reverse iterator of the string class to iterate backwards through the collection and appends each character to the new string.

BTW: Your compile problems is due to the fact that the compiler needs to know the size of the array when compiling. Otherwise you have to allocate the array dynamically using new (c++) or malloc (c)

char* reversal = new char [num];

Thanks for all your help.

Pete.

char* reversal = new char [num+1];

Don't forget a C-style string (null terminated char array) needs that extra bit of space for the null terminating character. If it doesn't have a null it really isn't a "string" but rather simply a char array.

...and remember to always delete what you new.

See http://richelbilderbeek.nl/CppReverseString.htm

std::string ReverseString(const std::string& s)
{
  std::string t;
  std::copy(s.rbegin(),s.rend(),std::back_inserter(t));
  return t;
}

Can be rewritten simply as:

std::string ReverseString(const std::string& s)
{
  return std::string(s.rbegin(),s.rend());
}

...and, put that way, it almost doesn't even seem to deserve its own function.

: ...and, put that way, it almost doesn't even seem to deserve its own
: function.
I purposefully post 'trivial' code on my website (http://richelbilderbeek.nl/CppWhyTrivialCode.htm): the beginner finds what he/she is looking for. The more advanced programmers use the one-line equivalent in his/her code directly.

P.S. I put your shorter version on my site and thanked you for it: http://richelbilderbeek.nl/CppReverseString.htm

If you would not mind...

Thanks, Bilderbikkel

i want know loop return... how does it work??
if we dom't use it, how do this code do?
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i want know loop return... how does it work??
if we dom't use it, how do this code do?
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