Solved

Negative Dec to Binary

Posted on 2004-08-08
5
428 Views
Last Modified: 2012-06-27
Below is my program that reads decimal numbers and outputs them in binary code.  Know I am trying to read negative numbers and output them in 2's complement form.  For example, 8 is 0000000000001000 but -8 is 1111111111111000 in 2's complement form.  How can I do this.  I tried changing the <> but this did not work.  
my input has these numbers 252,8,9,45,63,74 (uses these numbers for negative as well).

#include <iostream>
#include <fstream>

using namespace std;

void dectobin(int num, int base, int count = 0);

int main()
{
      ifstream inFile;
      inFile.open("input3.txt");
      
      int decimalnum[6];
      int base;
      int i;
      base = 2;
      
      cout<<"Enter the number in decimal: "<<endl;
      if(!inFile)
      {
            cout<<"Cannot open input file!"<<endl;
            return 1;
      }
      else
            for (i=0 ;i<6;i++) {
                  inFile>>decimalnum[i];
                  cout<<"Decimal: "<<decimalnum[i]<<" = ";
                  dectobin(decimalnum[i], base);
                  cout<< " in Binary" <<endl;
            }
            
            return 0;
            
}
void dectobin(int num, int base, int count)
{
      if(num > 0 || count < 16)
      {
            dectobin(num/base, base, ++count);
            cout<<num % base;
            
      }
      
}
0
Comment
Question by:Steve3164
  • 2
  • 2
5 Comments
 
LVL 55

Expert Comment

by:Jaime Olivares
ID: 11747860
Just manage the number always as unsigned

unsigned int unum = *((unsigned int *)yournumber);

That will catch your negative number without trying to make any conversion. If you print unum as usual will show you 2's complement.
0
 
LVL 39

Expert Comment

by:itsmeandnobodyelse
ID: 11748605
jaime has it right.

As a binary representation always is unsigned, change your prog that way:

#include <iostream>
#include <fstream>

using namespace std;

void dectobin(int num, int base, int count = 0);

int main()
{
     ifstream inFile;
     inFile.open("input3.txt");
     
     int decimalnum[6];
     int base;
     int i;
     base = 2;
     
     cout<<"Enter the number in decimal: "<<endl;
     if(!inFile)
     {
          cout<<"Cannot open input file!"<<endl;
          return 1;
     }
     else
          for (i=0 ;i<6;i++) {
               inFile>>decimalnum[i];
               cout<<"Decimal: "<<decimalnum[i]<<" = ";
               dectobin(decimalnum[i], base);
               cout<< " in Binary" <<endl;
          }
         
          return 0;
         
}
void dectobin(int inp, int base, int count)
{
     unsigned int num = (unsigned int)inp;
     if(num > 0 || count < 16)
     {
          dectobin(num/base, base, ++count);
          cout<<num % base;
         
     }
     
}


Regards, Alex

0
 

Author Comment

by:Steve3164
ID: 11749818
Alex,  

Your information help out but it outputs 32 bits for the negative and I need it to output only 16.  For example, -8 = 1111111111111000 but I get
11111111111111111111111111111000.  How can I do this?
0
 
LVL 39

Accepted Solution

by:
itsmeandnobodyelse earned 400 total points
ID: 11751051
Sorry, my fault.

Try that:

void dectobin(int inp, int base, int count)
{
     // first cast to 16 bits signed, then to 16 bits unsigned
     unsigned short num = (unsigned short)(short)inp;
     if(num > 0 || count < 16)
     {
          dectobin(num/base, base, ++count);
          cout<<num % base;
         
     }
}

Regards, Alex
0
 
LVL 55

Expert Comment

by:Jaime Olivares
ID: 11756719
Maybe I have not contributed to solve this problem?
0

Featured Post

Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

In days of old, returning something by value from a function in C++ was necessarily avoided because it would, invariably, involve one or even two copies of the object being created and potentially costly calls to a copy-constructor and destructor. A…
What is C++ STL?: STL stands for Standard Template Library and is a part of standard C++ libraries. It contains many useful data structures (containers) and algorithms, which can spare you a lot of the time. Today we will look at the STL Vector. …
The viewer will be introduced to the technique of using vectors in C++. The video will cover how to define a vector, store values in the vector and retrieve data from the values stored in the vector.
The viewer will be introduced to the member functions push_back and pop_back of the vector class. The video will teach the difference between the two as well as how to use each one along with its functionality.

756 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question