题解 | #学英语#

#include <iostream>
using namespace std;
void three(string s);
void learn(string s);
int main() {
    int a;
    cin>>a;
    string s=to_string(a);
    learn(s);
    return 0;
}

void learn(string s){
    int number;
    if(s.length()%3==0){
        number=s.length()/3-1;
    }
    else{number=s.length()/3;}
    if(number==0){
        three(s);
    }
    if(number>0){
        int x=s.length()-number*3;

        if(number==1){
            three(s.substr(0,x));
            cout<<"thousand ";
        }
        if(number==2){
            three(s.substr(0,x));
            cout<<"million ";
        }
        if(number==3){
            three(s.substr(0,x));
            cout<<"billion ";
        }
        learn(s.substr(x));
    }
}
void three(string s){
    int value=stoi(s);
    if(value<=9){
        switch(value){
            case 1:cout<<"one ";break;
            case 2:cout<<"two ";break;
            case 3:cout<<"three ";break;
            case 4:cout<<"four ";break;
            case 5:cout<<"five ";break;
            case 6:cout<<"six ";break;
            case 7:cout<<"seven ";break;
            case 8:cout<<"eight ";break;
            case 9:cout<<"nine ";break;
            default: break;
        }
    }
    if (value>=10&&value<=19){
        switch(value){
            case 10:cout<<"ten ";break;
            case 11:cout<<"eleven ";break;
            case 12:cout<<"twelve ";break;
            case 13:cout<<"thirteen ";break;
            case 14:cout<<"fourteen ";break;
            case 15:cout<<"fifteen ";break;
            case 16:cout<<"sixteen ";break;
            case 17:cout<<"seventeen ";break;
            case 18:cout<<"eighteen ";break;
            case 19:cout<<"nineteen ";break;
            default: break;
        }
    }
    if (value>=20&&value<=99){
        switch(s[0]){
            case '2':cout<<"twenty ";break;
            case '3':cout<<"thirty ";break;
            case '4':cout<<"forty ";break;
            case '5':cout<<"fifty ";break;
            case '6':cout<<"sixty ";break;
            case '7':cout<<"seventy ";break;
            case '8':cout<<"eighty ";break;
            case '9':cout<<"ninety ";break;
            default:break;
        }
        s=s.substr(1);
        three(s);
    }
    if(value==100){cout<<"one hundred ";}
    if(value>100){
        switch(s[0]){
            case '1':cout<<"one hundred and ";break;
            case '2':cout<<"two hundred and ";break;
            case '3':cout<<"three hundred and ";break;
            case '4':cout<<"four hundred and ";break;
            case '5':cout<<"five hundred and ";break;
            case '6':cout<<"six hundred and ";break;
            case '7':cout<<"seven hundred and ";break;
            case '8':cout<<"eight hundred and ";break;
            case '9':cout<<"nine hundred and ";break;
            default:break;
        }
        three(s.substr(1));
    }
}
// 64 位输出请用 printf("%lld")