机试复习

1、进制转换

①x进制转十进制

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

int main()
{
    char s[100010];
    scanf("%s", &s);
    int cnt = strlen(s);
    long long ans = 0;
    for (int i = 0; i < cnt; i ++ )
    {
        ans = ans * 16;                     //16可以更换为其他进制
        if (s[i] > '0' && s[i] < '9')       //若该字符在'0' ~ '9'之间 
            ans += s[i] - '0';
        else if (s[i] > 'a' && s[i] < 'z')  //若该字符为小写字母
            ans += s[i] - 'a' + 10;
        else ans += s[i] - 'A' + 10;        //若该字符为大写字母
    }   
    cout << ans;
}

②x进制转y进制

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 100010;

char s[N], out[N];
int cnt;
long long ans;

int main()
{
    //x进制转y进制
    int x = 2, y = 16;
    scanf("%s", &s);
    cnt = strlen(s);
    for (int i = 0; i < cnt; i ++ )
    {
        ans = ans * x;         

        //若该字符在'0' ~ '9'之间 
        if (s[i] >= '0' && s[i] <= '9') ans += s[i] - '0';

        //若该字符为小写字母
        else if (s[i] >= 'a' && s[i] <= 'z') ans += s[i] - 'a' + 10;

        //若该字符为大写字母
        else ans += s[i] - 'A' + 10;        
    }   
    cout << ans << endl;

    cnt = 0;
    while (ans > 0)
    {
        int w = ans % y;

        //若该字符在10以内
        if (w < 10) out[cnt ++ ] = w + '0';

        //若该字符为小写字母
        else if (w >= 'a' && w <= 'z') out[cnt ++ ] = (w - 10) + 'a';

        //若该字符为大写字母
        else out[cnt ++ ] = (w - 10) + 'A';

        ans /= y;
    }
    for (int i = cnt - 1; i >= 0; i -- )
        printf("%c", out[i]);
    printf("\n");
    return 0;
}