Inverse number (Leading zeroes)

[Oriol Serrabassa]

As you may know, this program is to inverse numbers (45 -> 54). However, there is a problem. With leading zeroes it does not work properly since integers ignore leading zeroes.

I read in Internet that to make this program work I should work with the text value and to do that I have to read the input into the string, then call std::reverse() and pass the string as input.

The problem is that I do not know how to do that. Can anyone teach me?

I cannot use any other library than iostream and string. Saying this because I saw other methods that use sstream library.

#include <iostream>
using namespace std;

int main () {
	int n;
	cin >> n;
	int reverse = 0;

	while (n != 0) {
		int remainder = n%10;
		reverse = reverse*10 + remainder;
		n /= 10;	
	}
	cout << reverse << endl;
}

[TarikNeaj]

#include <iostream>
#include <string>
#include <algorithm> // Forgot to include this one
using namespace std;

int main()
{
	
	string str1;
	cin >> str1;
	 
	std::reverse(str1.begin(), str1.end()); // Reverse beginning to end

	cout << str1 << endl;

	return 0;
}

Edit: Forgot to include <algorithm> for the std::reverse function.

[Oriol Serrabassa]

Your program does not compile TarikNeaj:

s.cc: In function ‘int main()’:
s.cc:12:2: error: ‘reverse’ is not a member of ‘std’
std::reverse(str1.begin(), str1.end()); // Reverse beginning to end
^

[TarikNeaj]

#include <iostream>
#include <string>
#include <algorithm> // Forgot to include this one

using namespace std;

int main()
{
	
	string str1;
	cin >> str1;
	 
	std::reverse(str1.begin(), str1.end()); // Reverse beginning to end

	cout << str1 << endl;

	return 0;
}

[Oriol Serrabassa]

Cannot use any other library than iostream and string because my exercise says so.

Is there another way to do it with only using iostream and string?

[LA48b7Xj]

#include <iostream>
#include <string>
using namespace std;

int main()
{
    string s;
    cin >> s;

    string rs;

    for(auto it = s.rbegin(); it != s.rend(); ++it)
        rs.push_back(*it);

    cout << rs << '\n';
}

[Oriol Serrabassa]

Program does not compile:

error: ‘it’ does not name a type
for(auto it = s.rbegin(); it != s.rend(); ++it)
^
error: expected ‘;’ before ‘it’
for(auto it = s.rbegin(); it != s.rend(); ++it)
^
error: ‘it’ was not declared in this scope

[LA48b7Xj]

change auto to string::reverse_iterator (auto is a C++'11 feature)

[Oriol Serrabassa]

Okay now it works.

I understand what the program does except for: rs.push_back(*it);

What does "rs.push_back(*it);" do?

[LA48b7Xj]

push_back is just adding characters to the end of the string, we are going through string s in reverse order, adding each character to string rs as we go.

If you wanted you could write rs += *it; instead.

Iterators are similar to pointers, using * on 'it' gives you access to what 'it' refers to.