POJ3070 Matrix Fast Power Template

Subject: http://poj.org/problem?id=3070

Matrix quick power template. mod is written to the definition part of multiplication.

Don't forget that I( ) and init( ) are pass-by-reference!

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
int n,p=10000;
struct Matrix{
    int a[2][2];
    Matrix operator *(const Matrix &b)const
    {
        Matrix c;
        c.a[0][0]=c.a[1][0]=c.a[0][1]=c.a[1][1]=0;
        for(int i=0;i<=1;i++)
            for(int j=0;j<=1;j++)
                for(int k=0;k<=1;k++)
                    (c.a[i][j]+=a[i][k]*b.a[k][j])%=p;
//                        printf("i=%d j=%d c=%d\n",i,j,b.a[i][j]);
        return c;
    }
};
Matrix r,u;
void I(Matrix &k)
{
    k.a[0][0]=k.a[1][1]=1;
    k.a[0][1]=k.a[1][0]=0;
}
void init(Matrix &k)
{
    k.a[0][0]=k.a[0][1]=k.a[1][0]=1;
    k.a[1][1]=0;
}
intmain ()
{
    while(1)
    {
        scanf("%d",&n);if(n==-1)return 0;
        if(!n){printf("0\n");continue;}
        n--;I(r);init(u);
        while(n)
        {
            if(n&1)r=r*u;
            n>>=1;u=u*u;
        }
        printf("%d\n",(r.a[1][0]+r.a[1][1])%p);
    }
}