在c ++中，如何确定将八进制数字转换为十进制时何时退出循环？

Question

Please keep in mind that I am pretty much brand new to C++ and this is just a program i have to do for my class. I think i understand how I would actually do it. I am just not sure what to put as my control condition for my while loop. I am supposed to be able to convert any octal number given, so how do know when I'm at the first number and should stop? I am moving forward numbers from right to left using increasing units of %10 (aka %10, %100,%1000), but how do I know when I should stop doing that? Like for the number 112 I would need to do %10, %100, and %100, but not past that.

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

int main ()
{
  cout <<"Please enter the octal number to be converted: " <<
  int octal;
  cin >> octal;

   int remainder = 0;
   int modular = 10;

  int conversionToDecimal = 0; 
  while(modular < ***********)
  remainder = octal%modular;
  if (remainder < 10)
  {
   conversionToDecimal = conversionToDecimal + (remainder *(int)pow(8.0,count));
    count = 0;
    modular = modular*10;
  }
  else
  {
    remainder = remainder/10;
    count++;
  }

Obviously the program is not complete that is just the code I got to when I discovered my problem. I put the * where I am needing help with the code. Thanks so much! In short, how should I control my loop so that I do not step off the front of the octal number?

Answer 1

You could use the same way as when converting a number to a string of decimal digits: An array with a digit per index. For each iteration, you take the modulo of 10, and store that digit, then divide by 10. When then number is zero (at the end of the loop), you're done.

Then take a digit at a time out of the array, and multiply your "total" by 8, add the current digit. When you have no more digits left, you're done.

I'll leave it to you to write the actual code to do this - after all, you're the one learning programming - I've been doing it for 30+ years.