Brief description of high precision

I recently opened a CSDN blog. On the one hand, I want to learn from the resources of CSDN, and on the other hand, I want to use this blog to record the road.
Let's talk about high precision:
High precision is also called a large integer, which is a number beyond the data range of integer (int) or even (longlong). (The range of int is -2147483648, the range of 2147483647/long long is -922 3372 0368 5477 5808 ~ 922 3372 0368 5477 5807)
There is an idea to turn large numbers into string input.
A+B Problem (High Precision)

#include<bits/stdc++.h>
using namespace std;

#define ma 100000
string x,y;
int a[ma],b[ma],c[ma],la,lb,lc;
int main ()
{
    
    
    cin >>x>>y;
    la= x.length();
    lb= y.length();
    for (int i=0; i<la; i++)
        a[la-i]=x[i]-'0';
    for (int j=0; j<lb; j++)
        b[lb-j]=y[j]-'0';
    lc=max(la,lb);
    for (int k=1; k<=lc; k++)
    {
    
    
        c[k]+=a[k]+b[k];
        c[k+1]=c[k]/10;
        c[k]%=10;
    }
    if (c[lc+1]>0)
        lc++;
    for (int i=lc; i>0; i--)
        cout << c[i];
    return 0;
}

length() means the length of the
string string a;
int main ()
{ int n; cin >>a;//input asc n = a.length(); cout <<n;//output 3 return 0; } Subtraction is similar to addition. A*B Problem

#include<bits/stdc++.h>
using namespace std;

#define ma 100000
string x,y;
int a[ma],b[ma],c[ma],la,lb,lc;
int main ()
{
    
    
    cin >> x>>y;
    la = x.length ();
    lb = y.length ();
    for (int i=0; i<la; i++)
        a[la-i]=x[i]-'0';
    for (int i=0; i<lb; i++)
        b[lb-i]=y[i]-'0';
    lc = la+lb;
    for (int i=1; i<=la; i++)
    {
    
    
        for (int j=1; j<=lb; j++)
        {
    
    
            c[i+j-1]+=a[i]*b[j];
            c[i+j]+=c[i+j-1]/10;
            c[i+j-1]%=10;
        }
    }
    while (c[lc]==0&&lc >1)lc--;
    for (int i=lc; i>0; i--)
        cout <<c[i];
    return 0;
}

       c[i+j-1]+=a[i]*b[j];

Every time you multiply, you have to go one bit to the first
c[i+j]+=c[i+j-1]/10;
c[i+j-1]%=10;
there is a carry, and 1 cut 10 ；