CODEWITHSUNDEEP
c++bit-manipulationmask
Oont
Oont

Reputation: 1

Using Bitwise to make Binary numbers (C++)

The assignment I attempted to do is past its due date, so you are not doing my homework.

For the sake of learning, I would like to know how to do a few things.

I was able to make a program, with a mask using bitwise operators print out 1-32 in binary.

The problem with the mask I used is that it would also print out 32 leading zeros, followed by the binary number (ex. 0000000000000000000000000000000001 for the number 1)

This is what I had 

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

    string naiveBitToChar( int num ) 
    {

string st;
unsigned mask = 0x80000000;

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

while( ( num & mask ) )
    mask >>= 1;
do 
{
    if ( num & mask ) 
    {
        st = st + "1";
    } 
        else 
        {
            st = st + "0";
        }

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


return st;
    }


    int main ( int argc, char* argv[] ) {

argc; argv;

    for( int i = 0; i < 32; i++ )
        cout << naiveBitToChar(i) << "\n";
    system ("pause");
    }

I needed to:

  1. Remove the leading zeros from the string
  2. Add a minimum width of 8 numbers in each string (ex. 00000010)
  3. Add underscores after every 4th number, by using a seperator mask (ex. 0000_1000)

I am new to C++, my teacher would not even look at my code, please someone explain, and try to keep it basic. Thank you!

Upvotes: 0

Views: 1021

Answers (2)

Slava
Slava

Reputation: 44238

If you scan from right to left, then it will be easier, as you do not need to remove leading zeros, but just to stop when number is 0:

std::string binary( unsigned n )
{
    std::string bits;
    for( unsigned mask = 1; true; mask <<=1 ) {
        bits.insert( bits.begin(), n & mask ? '1' : '0' );
        n &= ~mask;
        if( !n ) break;
    }
    return bits;
}

Or even simpler:

std::string binary( unsigned n )
{
    std::string bits;
    do {
        bits.insert( bits.begin(), n & 1 ? '1' : '0' );
        n >>= 1;
    } while( n );
    return bits;
}

To change minimum witdth you would need to modify loop condition slightly, to add unserscore can be as simple as:

if( bits.length() % 4 ) bits.insert( bits.begin(), '_' );

inside loop

Upvotes: 0

Thomas Matthews
Thomas Matthews

Reputation: 57678

Here's an idea, use a flag to indicate a leading zero digit. Change the flag if the bit is a one. Print the digit only if it is not a leading zero. 

bool is_leading_zero = true;
while (/*... */)
{
  // Convert bit to character in st
  if (st == '1')
  {
    is_leading_zero = false;
  }
  if (!is_leading_zero)
  {
    cout << st;
  }
}

Upvotes: 1

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