CODEWITHSUNDEEP
c++bigint
Neil
Neil

Reputation: 43

Bigint +operator

I'm doing a bigint project and I am stumped as to why my addition operator isn't working properly on a test case.

I'm excluding the .h file because its probably unnecessary.

bigint.cpp

#include "bigint.h"
#include<iostream>
#include<fstream>
#include<cstdlib>
#include<cassert>



bigint::bigint()
{                           //Default constructor that sets digit to ZERO
   for (int i = 0; i < MAX; i++) 
   {
     digits[i] = 0;
   }
 }


bigint::bigint(int n)
{

for(int i = 0; i < MAX; ++i)       //Sets the digit to ZERO
    digits[i] = 0; 

    for (int i = 0; n != 0 ; ++i) 
{
    digits[i] = (n % 10);       //
           n = n / 10;
}


}


bigint::bigint(const char new_digits[])  
{
int null = 0;
int temp = 0;

for(int i = 0; i < MAX; ++i)
{
    digits[i] = 0;
}

while(new_digits[null] != '\0')
    ++null;
    --null;
temp = null;

for(int j = 0; j < MAX && temp >= 0; ++j)
{
    digits[j] = new_digits[temp] - '0';
    temp -= 1;
}
}


bool bigint::operator==(const bigint& equal) const
{
int i = 0;

while(i < MAX)
{
    if(digits[i] != equal.digits[i])
    {
        return false;
    }

    ++i;
}
return true;
}


std::ostream& operator<<(std::ostream& output, const bigint& source)
{

int sub1 = MAX - 1; //subtracts 1 from the maximum size 

while(source.digits[sub1] == 0)
{
    --sub1;                            //EMPTY
}

while(sub1 > -1)
{
    output << source.digits[sub1]; 
    --sub1;
}

std::cout << std:: endl;

return output; 
}

std::istream& operator>>(std::istream& in, bigint& source)
{
char getdata[MAX];
char user_input;
int i = 0;



    in.get(user_input);
    while(!in.eof() && user_input != ';')
{
    in.get(user_input);
    source.digits[i] = user_input;
    ++i;
}

    source = bigint(getdata);

    return in;
}

char bigint::operator[](const int i)
{
return digits[i];
}

bigint bigint::operator+(const bigint rhs)
{
   bigint result;
    int i = 0;

    for( ; i < MAX; ++i) 
    {

        if((digits[i] + rhs.digits[i]) > 9)
        {
             digits[i+1] = digits[i+1] + 1 ;


        }

               result.digits[i] = (digits[i] + rhs.digits[i]);
               result.digits[i] = result.digits[i] % 10;
     }

    return result;




}

Main.cpp (Test case)

int main()
{
          // Setup fixture
    bigint left("1");
    bigint right("9");
    bigint result;

    // Test 
    result = (left + right);

     Verify
   assert(left   == "1");
   assert(right  == "9");
   assert(result == "10");

}

In this test case the program aborts at assert(result == "10");

but if I have the same test case except with assert(result == 10); the program runs.

Can anyone say why?

Upvotes: 1

Views: 3351

Answers (1)

Borealid
Borealid

Reputation: 98469

First off, you should implement bigint::operator=(const bigint&), the assignment operator.

Now, in operator+, you're altering the contents of the left-hand side object, in this code:

if((digits[i] + rhs.digits[i]) > 9)
{
     digits[i+1] = digits[i+1] + 1 ;
}

That's not good. For example, if you ran this code:

bigint x("5");
bigint y("6");

x+y;
x+y;

You would end up with x being 17.

Next, you're passing by value for the bigint::operator arguments where you should probably pass by reference (&).

Finally, your indentation here is actively malicious:

while(new_digits[null] != '\0')
    ++null;
    --null;

What is in the loop body here? That's right, not the third line. Please don't indent code like that, it makes kittens cry. Programming kittens, at least.

NB: I don't see any dynamic memory allocation code here, which means digits is probably a statically-sized array. Make sure it's big enough if you're going to do that and be aware you'll break if its size is exceeded.

Upvotes: 3

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