题解 | #数字阶梯求和#

#include <cstring>
#include <iostream>
using namespace std;
const int maxn=200;
struct bigint{
    int digit[maxn];
    int length;
    bigint();
    bigint(int x){
        length=0;
        memset(digit,0,sizeof(digit));
        if(x==0) digit[length++]=x;
        else {
            while(x>0){
                digit[length++]=x%10;
                x/=10;
            }
        }
    }
    bigint(int x,int n);
    bigint operator+(const bigint& b);
    bigint operator=(const bigint& b);
};
bigint::bigint() {
	memset(digit,0,sizeof(digit));
	length=0;
}
bigint bigint::operator+(const bigint& b){
    bigint answer;
    int carry=0;
    for(int i=0;i<length || i<b.length;i++){
        int c=digit[i]+b.digit[i]+carry;
        answer.digit[answer.length++]=c%10;
        carry=c/10;
    }
    if (carry!=0){
        answer.digit[answer.length++]=carry;
    }
    return answer;
}
bigint::bigint(int x,int n){
	memset(digit,0,sizeof(digit));
	length=0;
	while(n>0){
	digit[length++]=x;
	n--;}
} 
bigint bigint::operator=(const bigint& b){
	memset(digit,0,sizeof(digit));
	length=b.length;
	for(int i=0;i<b.length;i++) digit[i]=b.digit[i];
	return *this;
} 
int main() {
    int a, n;
    while (cin >> a >> n) { 
        bigint r;
        while(n>0) {
        	bigint c(a,n);
        	r=r+c;
        	n--;
		}
        for(int i=r.length-1;i>=0;i--) cout<<r.digit[i];
        cout<<endl;
    }
}