Till last 1 year, I search Big integer which works the same as an integer. Suppose it will directly support all arithmetic operations, assigning value in various ways, such as from integer, Long long, string, using (), etc. I found some code that Builds Big Integer using Vector/String. Which will take a problem when using regular vector/String in the same code. So, I build a Big Integer data type with my concept.

It builds with structure. Here used most of the arithmetic (+,-,/,*) logic from the LightOJ forum, written by Jane Alom Jan. Because whether I write the code and exist there some bugs. This BigInteger using system is same as the integer data type. But it has an unlimited range (actually limit of a string size). Because here used string as a number in BigInt. It doesn't support initializing value when declaring a variable.

Suppose, BigInt a=123, b="3435"; will not work. But you can use as, BitInt a("123"), b=BigInt("3435"), c=BigInt(3435); Supported operations are: Arithmetic: +, +=, X++, ++X, -, -=, X--, --X, *, *=, /, /=. Logical: <, <=, >. >=, ==, !=. Functions: pow(base,pw), pow(base,pw,mod), sqrt() ect. 3 way to possible initialize value: 1. i. Using BigInt. (n=b) ii. Using string. (n="1234") iii. Using Long Long int or Int. (n=12445) Also support cin>> to input from user. (cin>>a>>b;) 2 way to possible output: i. using cout. (cout<<a<<b<<c<<endl;).

And I'm not an expert in English. So maybe, there have some Grammatical Mistakes. I'm so sorry about that.

Tested submission: - 66026737 - 66026737

This is the code: Github Link: https://github.com/Riz1ahmed/Algorithms/blob/master/BigInteger%20by%20Riz1Ahmed.cpp

#include<bits/stdc++.h>
using ll=long long int;
using namespace std;

struct Bigint {
    string a;
    int sign;

    Bigint(){}
    void operator = (string b) {
        a= (b[0]=='-' ? b.substr(1) : b);
        reverse(a.begin(), a.end());
        (*this).Remove0(b[0]=='-' ? -1 : 1);
    }
    Bigint(string x) {(*this)=x;}
    Bigint(ll x) {(*this)=to_string(x);}
    void operator = (ll x){*this=to_string(x);}

    char operator[](int i){return a[i];}
    int size() {return a.size();}
    Bigint inverseSign() {sign*=-1; return (*this);}

    Bigint Remove0(int newSign) {
        sign = newSign;
        for(int i=a.size()-1; i>0 && a[i]=='0'; i--) a.pop_back();
        if(a.size()==1 && a[0]=='0') sign=1;
        return (*this);
    }

    bool operator == (Bigint x) {return sign==x.sign && a==x.a;}
    bool operator == (string x) {return *this==Bigint(x);}
    bool operator == (ll x)     {return *this==Bigint(x);}
    bool operator != (Bigint x) {return !(*this==x);}
    bool operator != (string x) {return !(*this==x);}
    bool operator != (ll x)     {return !(*this==x);}

    bool operator < (Bigint b) {
        if (sign!=b.sign) return sign<b.sign;
        if(a.size()!=b.size()) return a.size()*sign<b.size()*sign;
        for(int i=a.size()-1; i>=0; i--)
            if(a[i] != b[i]) return a[i]<b[i];
        return false;
    }
    bool operator <  (string x) {return *this<Bigint(x);}
    bool operator <  (ll x)     {return *this<Bigint(x);}
    bool operator <= (Bigint b) {return *this==b || *this<b;}
    bool operator <= (string b) {return *this==b || *this<b;}
    bool operator <= (ll b)     {return *this==b || *this<b;}
    bool operator >  (Bigint b) {return !(*this==b || *this<b);}
    bool operator >  (string x) {return !(*this==x || *this<x);}
    bool operator >  (ll b)     {return !(*this==b || *this<b);}
    bool operator >= (Bigint b) {return *this==b || *this>b;}
    bool operator >= (string b) {return *this==b || *this>b;}
    bool operator >= (ll b)     {return *this==b || *this>b;}

    Bigint operator + (Bigint b) {
        if(sign != b.sign) return (*this)-b.inverseSign();
        Bigint sum;
        for(int i=0, carry=0; i<a.size() || i<b.size() || carry; i++){
            if (i<a.size()) carry+=a[i]-'0';
            if (i<b.size()) carry+=b[i]-'0';
            sum.a += (carry % 10 + 48);
            carry /= 10;
        }
        return sum.Remove0(sign);
    }
    Bigint operator +  (string x) {return *this+Bigint(x);}
    Bigint operator +  (ll x)     {return *this+Bigint(x);}
    Bigint operator ++ (int) {*this+=1; return *this-1;}
    Bigint operator ++ ()    {*this+=1; return *this;}
      void operator += (Bigint x) {*this = *this+x;}
      void operator += (string x) {*this = *this+x;}
      void operator += (ll x)     {*this = *this+x;}


    Bigint operator - ( Bigint b ) {
        if(sign != b.sign) return (*this)+b.inverseSign();
        if(*this < b) return (b - *this).inverseSign();
        Bigint sub;
        for(int i=0,borrow=0; i<a.size(); i++) {
            borrow = a[i]-borrow-(i<b.size() ? b.a[i] : '0');
            sub.a += borrow>=0 ? borrow+'0' : borrow + 58;
            borrow = borrow>=0 ? 0:1;
        }
        return sub.Remove0(sign);
    }
    Bigint operator - (string x) {return *this-Bigint(x);}
    Bigint operator - (ll x)     {return *this-Bigint(x);}
    Bigint operator -- (int) {*this-=1; return *this+1;}
    Bigint operator -- ()    {*this-=1; return *this;}
      void operator -= (Bigint x) {*this = *this-x;}
      void operator -= (string x) {*this = *this-x;}
      void operator -= (ll x)     {*this = *this-x;}

    Bigint operator * (Bigint b) {
        Bigint mult("0");
        for(int i=0, k=a[i]; i<a.size(); i++, k=a[i]) {
            while(k-- -'0') mult=mult+b;
            b.a.insert(b.a.begin(),'0');
        }
        return mult.Remove0(sign * b.sign);
    }
    Bigint operator * (string x) {return *this*Bigint(x);}
    Bigint operator * (ll x)     {return *this*Bigint(x);}
      void operator *= (Bigint x) {*this = *this*x;}
      void operator *= (string x) {*this = *this*x;}
      void operator *= (ll x)     {*this = *this*x;}

    Bigint operator / (Bigint b) {
        if(b.size()==1 && b[0]=='0') b.a[0]/=(b[0]-'0');
        Bigint c("0"), d;
        for(int j=0; j<a.size(); j++) d.a += "0";
        int dSign = sign*b.sign; b.sign=1;
        for(int i=a.size()-1; i>=0; i--) {
            c.a.insert(c.a.begin(),'0');
            c=c+a.substr(i,1);
            while(!(c<b)) c=c-b, d.a[i]++;
        }
        return d.Remove0(dSign);
    }
    Bigint operator / (string x) {return *this/Bigint(x);}
    Bigint operator / (ll x)     {return *this/Bigint(x);}
      void operator /= (Bigint x) {*this = *this/x;}
      void operator /= (string x) {*this = *this/x;}
      void operator /= (ll x)     {*this = *this/x;}

    Bigint operator % (Bigint b) {
        if( b.size()==1 && b[0]=='0') b.a[0]/=(b[0]-'0') ;
        Bigint c("0");
        int cSign = sign*b.sign; b.sign=1;
        for( int i=a.size()-1; i>=0; i-- ) {
            c.a.insert( c.a.begin(),'0');
            c = c+a.substr(i,1);
            while(!(c<b)) c=c-b;
        }
        return c.Remove0(cSign);
    }
    Bigint operator % (string x) {return *this%Bigint(x);}
    Bigint operator % (ll x)     {return *this%Bigint(x);}
      void operator %= (Bigint x) {*this = *this%x;}
      void operator %= (string x) {*this = *this%x;}
      void operator %= (ll x)     {*this = *this%x;}

    void print() {
        if(sign==-1) putchar('-');
        for(int i=a.size()-1; i>=0; i--) putchar(a[i]);
    }
    friend istream& operator >>(istream &in,Bigint &x){
        string s; in>>s; x=s; return in;
    }
    friend ostream& operator <<(ostream &out,Bigint &x){
        if(x.sign==-1) putchar('-');
        for(int i=x.size()-1; i>=0; i--)
            putchar(x[i]);
        return out;
    }

    friend Bigint pow(Bigint base, Bigint pw){
        Bigint ans=1;
        while(pw!=0){
            if(pw%2 !=0) ans*=base;
            base*=base, pw/=2;
        }
        return ans;
    }
    friend Bigint pow(Bigint a, Bigint b,Bigint mod) {
        if (b==0) return Bigint(1);
        Bigint tmp=pow(a,b/2,mod);
        if ((b%2)==0) return (tmp*tmp)%mod;
        else return (((tmp*tmp)%mod)*a)%mod;
    }
    friend Bigint sqrt(Bigint x) {
        Bigint ans=x,tmp=(x+1)/2;
        while (tmp<ans) ans=tmp, tmp=(tmp+x/tmp)/2;
        return ans;
    }
    friend Bigint gcd(Bigint a,Bigint b){
        return a%b==0 ? b : gcd(b, a%b);
    }
    friend Bigint lcm(Bigint a,Bigint b){
        return a/gcd(a,b);
    }
};

int main(){
    Bigint a,b,n,ans,M=1000000007;
    cin>>a>>b>>n;
    ans=pow(a,b,n);
    cout<<ans<<endl;
}