Subtract Two Numbers Represented as Linked Lists in C++

This C++ program takes the values of two large numbers as input and displays the computed value node by node in the resultant linked list.

Here is the source code of the C++ program to display the subtraction of two large numbers using linked list. The C++ program is successfully compiled and run on DevCpp, a C++ compiler. The program output is also shown below.

```
/*
```

 * C++ Program to use Linked List and subtract two large Numbers

```
 */
```
```
#include<iostream>
```
```
#include<conio.h>
```
```
using namespace std;
```
```
int c = 0,c1 = 0;
```
```
struct node1
```
```
{
```
```
    node1 *link;
```
```
    int data1;
```

}*head = NULL, *m = NULL, *np1 = NULL, *n = NULL;

```
struct node
```
```
{
```
```
    node *next;
```
```
    int data;
```

}*start = NULL, *p = NULL, *np = NULL, *q = NULL;

```
void store(int x)
```
```
{
```
```
    np1 = new node1;
```
```
    np1->data1 = x;
```
```
    np1->link = NULL;
```
```
    if (c == 0)
```
```
    {
```
```
        head = np1;
```
```
        m = head;
```
```
        m->link = NULL;
```
```
        c++;
```
```
    }
```
```
    else
```
```
    {
```
```
        m = head;    
```
```
        while (m->link != NULL)
```
```
        {
```
```
            m = m->link;
```
```
        }
```
```
        m->link = np1;
```
```
        np1->link = NULL;          
```
```
    }
```
```
}
```
```
void keep(int x)
```
```
{
```
```
    np = new node;
```
```
    np->data = x;
```
```
    np->next = NULL;
```
```
    if (c1 == 0)
```
```
    {
```
```
        start = np;
```
```
        p = start;
```
```
        p->next = NULL;
```
```
        c1++;
```
```
    }
```
```
    else
```
```
    {
```
```
        p = start;
```
```
        while (p->next != NULL)
```
```
        {
```
```
            p = p->next;
```
```
        }
```
```
        p->next = np;
```
```
        np->next = NULL;            
```
```
    }   
```
```
}
```
```
void sub()
```
```
{
```
```
    int x;
```
```
    p = start;
```
```
    m = head;
```
```
    while (p != NULL)
```
```
    {
```
```
        if (p->data >= m->data1)
```
```
        {
```

            p->data = p->data - m->data1;

```
            p = p->next;
```
```
            m = m->link;
```
```
            continue;
```
```
        }
```
```
        else if (p->data < m->data1)
```
```
        {
```
```
            q = p;
```
```
            n = m;
```
```
            x = 0;
```
```
            do
```
```
            {
```

                if (q->data <= n->data1 && x == 0)

```
                {
```

                    q->data = q->data + 10;

```
                    q = q->next;
```
```
                    n = n->link;
```
```
                    x++;
```
```
                }
```

                else if (q->data <= n->data1 && x != 0)

```
                {
```

                    q->data = q->data + 9;

```
                    q = q->next;
```
```
                    n = n->link;
```
```
                    x++;
```
```
                }
```
```
                if (q->data > n->data1)
```
```
                {
```

                    q->data = q->data - 1;

```
                } 
```
```
            }   
```

            while (q->data  < n->data1);

```
        }
```
```
    }
```
```
}
```
```
void traverse()
```
```
{
```
```
    node *q = start;
```
```
    int c = 0, i = 0;
```
```
    while (q != NULL)
```
```
    {
```
```
        q = q->next;
```
```
        c++;
```
```
    }
```
```
    q = start;
```
```
    while (i != c)
```
```
    {
```
```
        x[c - i - 1] = q->data;
```
```
        i++;
```
```
        q = q->next;
```
```
    }
```

    cout<<"Result of subtraction for two numbers:\t";

```
    for (i = 0; i < c; i++)
```
```
    {
```
```
        cout<<x[i]<<"\t";
```
```
    }
```
```
}
```
```
void swap(int *a,int *b)
```
```
{
```
```
    int temp;
```
```
    temp = *a;
```
```
    *a = *b;
```
```
    *b = temp;
```
```
}
```
```
int main()
```
```
{
```
```
    int n, x, mod, mod1;
```
```
    int n1 = 0, n2 = 0;
```

    cout<<"Enter the two numbers"<<endl;

```
    cin>>n;
```
```
    cin>>x;
```
```
    if (x > n)
```
```
    {
```
```
        swap(&x, &n);
```
```
    }
```
```
    while (n > 0)
```
```
    {
```
```
        mod = n % 10;
```
```
        n = n / 10;
```
```
        keep(mod);
```
```
        n1++;
```
```
    }
```
```
    while (x > 0)
```
```
    {
```
```
        mod1 = x % 10;
```
```
        x = x / 10;
```
```
        store(mod1);
```
```
        n2++;
```
```
    }
```
```
    n1 = n1 - n2;
```
```
    while (n1 > 0)
```
```
    {
```
```
        store(0);
```
```
        n1--;
```
```
    }
```
```
    sub();
```
```
    traverse();
```
```
    getch();
```
```
}
```

 
Output
 
Enter the two numbers
2567
989
Result of subtraction for two numbers:  1       5       7       8

Sanfoundry Global Education & Learning Series – 1000 C++ Programs.

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