Why doesn't code reverse string?

[Mechennyy]

Hello everyone, I unfortunately had to take a little break from learning programming so I have forgotten a few things and a little rusty, so I apologize if the answer is blatantly obvious.

I had to write a small program that takes a string that the user enters and reverses it. After spending awhile trying I got it working with this...

#include <iostream>
#include <string>

using namespace std;

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

	cout << "Please enter a string: ";
	getline(cin, s);

	for (int i = 0; i < s.length(); i++)
		r = s[i] + r;

	cout << "Reversed string = " << r << endl;

	cout << endl;
	system("Pause");
	return 0;
}

But before I got that I came up with this...

#include <iostream>
#include <string>

using namespace std;

int main()
{
	string s = "";
	int cnt = 0;

	cout << "Please enter a string: ";
	getline(cin, s);

	string r = s;

	for (int i = s.length(); i > 0; i--)
	{
		r[cnt] = s[i];
		cnt++;
	}

	cout << "Reversed string = " << r << endl;

	cout << endl;
	system("Pause");
	return 0;
}

It reverses most of the string but doesn't show the first character of the original string. For instance Hello comes out as olle. I've also tried some slight variations such as..

for (int i = s.length() + 1; i > 0; i--)
for (int i = s.length(); i >= 0; i--)

I am wondering why this code won't work correctly it seems like it should to me.


Thanks.

[2UD8vCM9]

Maybe this will help

string original = "original string";
string reversed;
for ( int count = original.size()-1; count>=0; count--)
{
   reversed += original [count];
} 

We start at size ()-1 because we can't access thr char at size () because there's nothing there. We check >=0 to make sure we include the first char

[jvqpDjzh]

You can do something like this:

std::string Reverse(std::string str="")
{
    if(str.length() > 1)//we don't need to reverse if the string is empty or 1
//it has to have at least 2 characters to make sense to reverse it
    {
        std::string newStr = "";
        for(int i=str.length() -1; i>=0; i--)
            newStr += str.at(i);
//at() is similar to str[i], but this last one doesn't throw an exception
        return newStr;
    }
    return str;//returns the string if its length <= 1
}

[j3Rz8vqX]

You'd want to assign "i" the last value, not its termination.
And you'd want to include its entry [0].

	for (int i = s.length()-1; i >= 0; i--)
	{
		r[cnt] = s[i];
		cnt++;
	}

Assumption:
string == "hello"
[0] = 'h'
[1] = 'e'
[2] = 'l'
[3] = 'l'
[4] = 'o'

s.length() returns [5], but you wanted [4] to be the first argument, otherwise you'd get: 'garbage'+'o'+'l'+'l'+'e'+'h' == [5][4][3][2][1][0]

And because [0] was not inclusive: i > 0;
you'd get: 'garbage'+'o'+'l'+'l'+'e' == [5][4][3][2][1]

[4][3][2][1][0] == 'o'+'l'+'l'+'e'+'h'

Welcome back.

[Mechennyy]

Thanks guys.

I can't believe I forgot about starting at 0 and the '\0' that would be at the very end of the string. Well, I didn't really forget since I started at 0 with..

int cnt = 0;
for (int i = s.length(); i > 0; i--)
	{
		r[cnt] = s[i];
		cnt++;
	}

So I'm really not sure how that slipped by.