Add two large number using array - c++

Question

sorry for my english.
I wrote a programm that add two large numbers.
Number 1 is read from file data1.in, the same with the second, data2.in.
The problem was when I tryed to add 68925579999999999990+79925579999999999990 I am getting the wrong result:48951159999999999980.
using python to add these numbers I have got 148851159999999999980.
Where I got wrong ??
#include <iostream.h>
#include <fstream.h>
#include<math.h>
int n = 0;
int m = 0;
const int zerou = 9000;
//using namespace std;
void zero(int*a)
{
for(int i = 0;i<zerou;i++)
a[i]=0;
}
void zero(int*a,int*b)
{
for(int i = 0;i<zerou;i++)
a[i]=b[i]=0;
}
void rebuild(int* a)
{
int temp[9000];
zero(temp);
int i;
int delta = abs(m-n)+1;//k1 -dim a
for(i = delta;i<n+delta;i++)
{
temp[i] = a[i-delta];
a[i-delta] = 0;
}
n += delta;
for(i =0;i<n;i++)
a[i] = temp[i];
}
void rebuildS(int* a)
{
int temp[9000];
zero(temp);
int i;
int delta = abs(m-n)+1;//k1 -dim a
for(i = delta;i<m+delta;i++)
{
temp[i] = a[i-delta];
}
m += delta;
for(i =0;i<m;i++)
a[i] = temp[i];
}
void citirea(int* ar){
ifstream f;
f.open("data1.in");
int data;
while (f>>data){
ar[n++] = data;
}
f.close();
}
void citirea_(int* ar){
ifstream f("data2.in");
int data;
while (f>>data){
ar[m++] = data;
}
f.close();
}
/*
void perDig(int*a, int*b,int *t,int i)
{
*t += (a[i]+b[i])/10;
a[i] = (a[i]+b[i]+*t)%10;
}*/
void adunarea(int*a, int* b)
{
int transport = 0;
int sum;
for(int i = n;i>=0;i--)
{
sum = a[i]+b[i]+transport;
//sum = perDig(a,b,transport,i);
if(sum >9)
{
transport = (sum)/10;
sum %=10;
}
a[i] = sum;
}
}
int main()
{
int a[9000],b[9000];
zero(a,b);
citirea(a);
citirea_(b);
if(n > m)
rebuildS(b);
else if(m > n)
rebuild(a);
adunarea(a,b);
ofstream rez;
rez.open("data.out");
for(int i = 0;i<m;i++)
{
rez<<a[i]<<" ";
}
rez.close();
cin.get();
return 0;
}

Answer 1

There are two errors in your answer.
if (!sum > 9) you don't zero the transport, so numbers carry forever.
You are going to be one digit short because you add N digits and don't account for an Nth+1 digit in the answer if transport != 0.
You have a bigger problem, though. You don't know how to debug the code yourself. If in doubt, make the program tell you each step it performs, and read what it says, and see where it goes wrong. Knowing how to do this is worth more than 10 correct versions of your code.
void adunarea(int*a, int* b)
{
int transport = 0;
int sum;
for(int i = n;i>=0;i--)
{
cout << a[i] << " + " << b[i] << " + " << transport << endl;
sum = a[i]+b[i]+transport;
if(sum >9)
{
transport = (sum)/10;
sum %=10;
}
a[i] = sum;
cout << " = " << sum << " ( " << transport << " )" << endl;
}
}
All I've done is add two print statements, and with that and the correct answer you can look for the first incorrect digit and see absolutely everything about how the wrong digit was made, and then fix it.