Decimal to binary (and vice-versa)

Question

Can anybody give an example of c++ code that can easily convert a decimal value to binary and a binary value to decimal please?

In what format? Strings? Numerical types don't care about base, since they're all stored as binary data regardless... — Amber, Mar 30 '10 at 20:04
it can be anything int...String...i was looking for smallest and efficient code. — Jony, Mar 30 '10 at 20:06
Likely duplicate: http://stackoverflow.com/questions/819487/efficiently-convert-between-hex-binary-and-decimal-in-c-c — mjv, Mar 30 '10 at 20:06
@Dav: I'm guessing Codeguru actually means that the input could be anything, but the output should be a string? — Cascabel, Mar 30 '10 at 20:08
@MaxGuernseyIII: LOL. Assuming UFC is as in "Ultimate Fighting", at least nobody would dare make fun of your handle... I couldn't resist here with our OP, a guru who doesn't find his way around google or a good reference book ;-) — mjv, Mar 30 '10 at 20:28

IVlad · Accepted Answer · 2010-03-30T20:36:03.473

Well, your question is really vague, so this answer is the same.

string DecToBin(int number)
{
    if ( number == 0 ) return "0";
    if ( number == 1 ) return "1";

    if ( number % 2 == 0 )
        return DecToBin(number / 2) + "0";
    else
        return DecToBin(number / 2) + "1";
}

int BinToDec(string number)
{
    int result = 0, pow = 1;
    for ( int i = number.length() - 1; i >= 0; --i, pow <<= 1 )
        result += (number[i] - '0') * pow;

    return result;
}

You should check for overflow and do input validation of course.

x << 1 == x * 2

Here's a way to convert to binary that uses a more "programming-like" approach rather than a "math-like" approach, for lack of a better description (the two are actually identical though, since this one just replaces divisions by right shifts, modulo by a bitwise and, recursion with a loop. It's kind of another way of thinking about it though, since this makes it obvious you are extracting the individual bits).

string DecToBin2(int number)
{
    string result = "";

    do
    {
        if ( (number & 1) == 0 )
            result += "0";
        else
            result += "1";

        number >>= 1;
    } while ( number );

    reverse(result.begin(), result.end());
    return result;
}

And here is how to do the conversion on paper:

What if we want to have a fixed length of binary number? For example, if we would like to have an 8 bit representation, then `1` has to be returned as `00000001`. — Rasoul, Sep 08 '13 at 16:10
@Rasoul - then just add leading zeros until you get your desired length. Some programming languages provide methods to do this out of the box. — IVlad, Sep 08 '13 at 16:13

score 2 · Answer 2 · answered Aug 06 '14 at 09:47

2

//The shortest solution to convert dec to bin in c++

void dec2bin(int a) {
    if(a!=0) dec2bin(a/2);
    if(a!=0) cout<<a%2;
}
int main() {
    int a;
    cout<<"Enter the number: "<<endl;
    cin>>a;
    dec2bin(a);
    return 0;

}

answered Aug 06 '14 at 09:47

NoriMax

21
1

score 2 · Answer 3 · answered Mar 30 '10 at 20:06

2

strtol will convert a binary string like "011101" to an internal value (which will normally be stored in binary as well, but you don't need to worry much about that). A normal conversion (e.g. operator<< with std:cout) will give the same value in decimal.

answered Mar 30 '10 at 20:06

Jerry Coffin

476,176
80
629
1,111

score 1 · Answer 4 · answered Mar 30 '10 at 22:52

I assume you want a string to binary conversion?

template<typename T> T stringTo( const std::string& s )
   {
      std::istringstream iss(s);
      T x;
      iss >> x;
      return x;
   };

template<typename T> inline std::string toString( const T& x )
   {
      std::ostringstream o;
      o << x;
      return o.str();
   }

use these like this:

int x = 32;
std:string decimal = toString<int>(x);
int y = stringTo<int>(decimal);

Decimal to binary (and vice-versa)

4 Answers4

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