How to solve this problem in subtract in biginteger class

Question

1.00/5 (1 vote)

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C++

class BigInteger
{
    public:
    void Subtraction()
    {
        string string1,string2;
        char x=0;
        cout<<"Enter first number :";
        cin>>string1;
        cout<<"Enter second number :";
        cin>>string2;
        size_t n=max(string1.size(),string2.size());
        if(n>string1.size())
            string1=string(n-string1.size(),'0')+string1;
        if(n>string2.size())
            string2=string(n-string2.size(),'0')+string2;
        string final(n,'0');
        string::const_reverse_iterator s1 = string1.rbegin(), e = string1.rend(), s2 = string2.rbegin();
        string::reverse_iterator f = final.rbegin();
        while (s1!=e)
        { 
            int ss1=*s1-'0';
            if(*s1-'0'<*s2-'0')
            {
                int m=ss1+10;
                ++s1;
                ss1--;
                --s1;
                x = m-(*s2-'0');
            }
            else 
            {
                x=ss1-(*s2-'0');	
            }
            *f = x + '0';
            ++s1;
            ++s2;
            ++f;     
        }
                       
        cout<< "final = " <<final << endl;
    }
};

when I enter number 1= 35
and number 2=6
the result = 39
in this line
ss1--;
the problem is when subtract one from second digit no change happened in the basic string

Posted 14-Dec-14 11:01am

Member 11303951

Updated 14-Dec-14 11:40am

Dave Kreskowiak

v2

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Comments

Sergey Alexandrovich Kryukov 14-Dec-14 18:53pm

The whole idea to implement big integers based on string representation is utterly bad, so why considering some particular bugs?

Make a correct start, then we can discuss it. Don't use decimal system. As nearly all CPUs are byte-based, but, for unlimited-size numbers, you still need to use digit-by-digit algorithms, you have to use 256-ary systems or perhapes any other with 2^2² base.

Also, your class makes sense at all. Get rid of I/O, implement only arithmetic, constructors creating your number from some of the integer types and string and implement "to string" formatting.

—SA

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KarstenK · Answer 1 · 2014-12-14T23:48:00

For mathematics you should convert the input string to a number ParseInt64 will do it for really big numbers.

C++

long number1 = Int64.Parse(string1);
long number2 = Int64.Parse(string1);
//and now do the math
long result = number1 - number2;

if you need bigger numbers, so must split the numbers from the right side.