Thread: simple but not working

Alright, thanks for the code examples above.
I will be studying them and will use them once I know and test them better.

Below is the hardway in that it demonstrates the math and could be extended to other bases.

As always your comments are welcome.

Dave++

Code:

#include <iostream>
#include <stdio.h>
#include <string>
#include <cmath>
#include <cstdlib>

std::string DecToBin(float num)
{
  std::string str = "";
  int i, expmax;
  double top;
  const double lg2 = log(2.0);

  if(num == 0) return("0");

  expmax = floor(log(num)/lg2);
  //  std::cout <<"expmax " << expmax << std::endl;

  for(i=expmax; i>=0; i--){
    top = num - pow(2.0,i);    // subtract the binary basis
    //    std::cout << num << " " << top << std::endl;
    if (top < 0){
      str = str + "0";
    }
    else {
      str = str + "1";
    num = top;
    }
  }
  return(str);
}      

int main()
{
  int num;
  printf("Enter a whole number: ");
  scanf("&#37;i", &num);
  std::cout << DecToBin(num) << std::endl; 
  //  std::cout << log(2.0) << std::endl;
}

____________
If there are no spoons, then where did all the ice cream come from? ("7")

To Dave++:

<stdio.h> is a C header file. Usually one uses <cstdio>, which puts the functions in <stdio.h> into the namespace std. I see you've included <cmath> instead of <math.h>, but you're using just plain pow() and log() etc. Use either <math.h> and pow() or <cmath> and std::pow.

Also,

Code:

str = str + "0";

is the same as

Code:

str += "0";

which means, of course, that you can use either. But the latter requires less typing and is less error-prone.

a = a + b and a += b may be semantically equivalent, but they might very well differ in efficiency. Typically, += is considerably more efficient.

For appending a single character, an alternative would be:

Code:

str.push_back('0');

You shouldn't return pointers to local objects, either. Returning objects by value is okay (assuming that the object has a proper copy constructor!) because the calling function gets a copy of the object.