C++代码：数组匹配

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

int a[]= {61,71,11,21,32,19,27,31};
string b[]= {"Brasilia","Salvador","Sao Paulo","Rio de Janeiro",
             "Juiz de Fora","Campinas","Vitoria","Belo Horizonte"
            };

int main() {
    int x;
    cin>>x;

    for(int i=0; i<8; i++) {
        if(x==a[i]) {
            cout<<b[i]<<endl;
            return 0;
        }
    }

    cout<<"DDD nao cadastrado"<<endl;

    return 0;
}

/*
in:11
out:Sao Paulo
*/

C++代码：结构体数组

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

struct City {
    int ddd;
    string des;
} c[8];

int main() {
    c[0].ddd=61,c[0].des="Brasilia";
    c[1].ddd=71,c[1].des="Salvador";
    c[2].ddd=11,c[2].des="Sao Paulo";
    c[3].ddd=21,c[3].des="Rio de Janeiro";
    c[4].ddd=32,c[4].des="Juiz de Fora";
    c[5].ddd=19,c[5].des="Campinas";
    c[6].ddd=27,c[6].des="Vitoria";
    c[7].ddd=31,c[7].des="Belo Horizonte";

    int x;
    cin>>x;
    for(int i=0; i<x; i++) {
        if(x==c[i].ddd) {
            cout<<c[i].des<<endl;
            return 0;
        }
    }

    cout<<"DDD nao cadastrado"<<endl;

    return 0;
}

/*
in:11
out:Sao Paulo
*/

C++代码：switch-case

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

int main() {
    int x;
    cin>>x;
    switch(x) {
        case 61:
            cout<<"Brasilia"<<endl;
            break;
        case 71:
            cout<<"Salvador"<<endl;
            break;
        case 11:
            cout<<"Sao Paulo"<<endl;
            break;
        case 21:
            cout<<"Rio de Janeiro"<<endl;
            break;
        case 32:
            cout<<"Juiz de Fora"<<endl;
            break;
        case 19:
            cout<<"Campinas"<<endl;
            break;
        case 27:
            cout<<"Vitoria"<<endl;
            break;
        case 31:
            cout<<"Belo Horizonte"<<endl;
            break;
        default:
            cout<<"DDD nao cadastrado"<<endl;
    }

    return 0;
}

/*
in:11
out:Sao Paulo
*/

C++代码：if-else if-else

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

int main() {
    int x;
    cin>>x;
    if(x==61) cout<<"Brasilia"<<endl;
    else if(x==71) cout<<"Salvador"<<endl;
    else if(x==11) cout<<"Sao Paulo"<<endl;
    else if(x==21) cout<<"Rio de Janeiro"<<endl;
    else if(x==32) cout<<"Juiz de Fora"<<endl;
    else if(x==19) cout<<"Campinas"<<endl;
    else if(x==27) cout<<"Vitoria"<<endl;
    else if(x==31) cout<<"Belo Horizonte"<<endl;
    else cout<<"DDD nao cadastrado"<<endl;

    return 0;
}

/*
in:11
out:Sao Paulo
*/