Question

I’m writing a function to return the reverse of a number i.e it converts int(1234) to int(4321). This is what I have currently:

#include <iostream>
#include <cstdlib>
#include <string>
#include <sstream>

using namespace std;


int reverse(int num) {
  stringstream ss (stringstream::in | stringstream::out);
  string initial; 
  int reversed;

  // read the number in to a string stream
  ss << num;
  initial = ss.str();

  // flush the stringstream
  ss.str("");
  for(unsigned int i(0); i <= initial.size(); i++) {
    ss << initial[initial.size() - i];
  }
  ss >> reversed;

  return reversed;
}


int main(int argc, const char *argv[])
{
  int test = 9871;
  cout << "test = " << test << endl;
  cout << "reverse = " << reverse(test) << endl;

  return 0;
}

However this just outputs:

test = 9871
reverse = 0

And I’m pretty certain the problem is in the line ss >> reversed is the problem in that reversed is being set to 0 instead of the value of ss, but I can’t figure out what’s wrong with this code, and it’s infuriating as it seems like it should be simple. Can anyone help?

Thanks

Answer 1

i starts from 0, then initial.size() - i is out of string bounds.

Change to ss << initial[initial.size() - i - 1]; and iterate i from 1 to initiali.size() - 1

for(unsigned i = 0; i != initial.size(); ++i) {
  ss << initial[initial.size() - i -1];
}

Or iterate i from 1 to initial.size()

for(unsigned i = 1; i <= initial.size(); ++i) {
  ss << initial[initial.size() - i];
}