Trouble with Big Number in C++

Trouble with Big Number in C++

Glane,

1. First of all, I would like to give you a suggestion. Try adding 2 numbers not by using (+) and also using string to store the numbers. Remember the old primary school arithmetic?
2. Add them 1 digit by 1 and move the carry. Simulate all the processes. This would be the back bone of your multiplication program.
3. Then just take a single digit (1st one) of the multiplier. Multiply it with the subject number( again old school arithmetic). Then the 2nd digit. And so on.
4. Finally, add them, just as you do when multiplying using pen and paper.

Trouble with Big Number in C++

Thanks for the reply. The program didn't compile at first. Had to add some library and a few braces. Unfortunately they gave a bad result.

Enter a number (up to 30 digits in length)> 123

The first number is: 123

Enter a second number (up to 30 digits in length)> 1

The second number is: 1

The sum of the two numbers is: 110-875710266-19147776507-9801854178-1194415713-406201652-474099748-672935959-1600219442-959534433-4734392825-980972948-303969823-609235240
-1331633444-911438227-1663054639-1063101776-875047979-1770211641-891100696-761550896-2065179199774

The product of the two numbers is: 000000000000000000000000000000000000000000000000000000000000201333116

Process returned 0 (0x0)   execution time : 4.213 s
Press any key to continue.

Thanks for the help any way. But I would like to go for making a simple one myself, for better understanding.

@AngelOfTech,

Thanks for the suggestion.  I have modularized the problem as you said. For first one I added 2 single digits( passed as characters along with carry) and added them to the first parameter. It will also return if there is any carry.

int addchar(char &a,char b,int carry=0)
{
    int p=((int)a+b-'0'-'0')+carry;
    a= (p%10)+'0';
        if(p>9)return 1;
    else return 0;
}

And adding as follows

void addBigInt(string &i1,string i2)
{
    reverse(i1.begin(),i1.end());                        //reversing makes it easy to align the digits. As we add the right most digits first.
    reverse(i2.begin(),i2.end());

    int carry=0;
    for(int i=0;i<i2.size();++i)
    {
        if(i>=i1.size())
        {
            i1+= "0";
            carry=addchar(i1[i],i2[i],carry);
        }
        else
        {
            carry=addchar(i1[i],i2[i],carry);
        }
    }
    if(carry!=0)i1+="1";
        reverse(i1.begin(),i1.end());
       reverse(i2.begin(),i2.end());
}

This is working good for,

1
+9999
=10000

but

9999
+  1
=19990

Can't find why.

Trouble with Big Number in C++

Thanks very much….

Here is my muliplier (single digit) very much like the adder

int multchar(char &a,int b,int carry=0)
{
    int p=(((int)a-'0')*b)+carry;
    a= (p%10)+'0';
        if(p>9)return (p/10);
    else return 0;
}

I am a little confused about how do i do a full multidigit multiplication multiplication?

Trouble with Big Number in C++

We have our adder ready. So we can just multiply 1 digit at a time and then finally add all the results.

Here is a startup for the function you made:

void multBigInt(string &i1,int i2)         //Multiply big integer with single digit
{
    reverse(i1.begin(),i1.end());
    int carry=0;
    for(int i=0;i<i1.size();++i)
    {
            carry=multchar(i1[i],i2,carry);
    }

    if(carry!=0)
    {
        i1+=" ";
        i1[sz(i1)-1]=carry+'0';
    }
    reverse(i1.begin(),i1.end());
}

You just have to call this one for all the digits in the multiplier and add them gradually.

Trouble with Big Number in C++

Thanks very much. It was very nice of all of you.