口算练习题

1. 无脑 if

#include <bits/stdc++.h>
using namespace std;
int cal(int x)
{
    bool flag = false;
    if (x < 0)
    {
        flag = true;
        x = -x;
    }
    if (0 <= x && x <= 9)
        return 1 + flag;
    else if (10 <= x && x <= 99)
        return 2 + flag;
    else if (100 <= x && x <= 999)
        return 3 + flag;
    else if (1000 <= x && x <= 9999)
        return 4 + flag;
    else if (10000 <= x && x <= 99999)
        return 5 + flag;
    else if (100000 <= x && x <= 999999)
        return 6 + flag;
    else if (1000000 <= x && x <= 9999999)
        return 7 + flag;
    else if (10000000 <= x && x <= 99999999)
        return 8 + flag;
    else if (100000000 <= x && x <= 999999999)
        return 9 + flag;
}
void f(char op, int a, int b)
{
    int c;
    if (op == 'a')
    {
        c = a + b;
        op = '+';
    }
    else if (op == 'b')
    {
        c = a - b;
        op = '-';
    }
    else if (op == 'c')
    {
        c = a * b;
        op = '*';
    }
    cout << a << op << b << "=" << c << "\n";
    cout << cal(a) + cal(b) + cal(c) + 2 << "\n";
}
int main()
{
    int n;
    cin >> n;
    char op;     // 运算符
    int a, b;    // 两个运算数
    string temp; // 临时字符串
    for (int i = 1; i <= n; i++)
    {
        cin >> temp;
        if ('0' <= temp[0] && temp[0] <= '9')
        {
            a = 0;
            for (int j = 0; j < temp.size(); j++)
                a = a * 10 + (temp[j] - '0');
            cin >> b;
        }
        else
        {
            op = temp[0];
            cin >> a;
            cin >> b;
        }
        f(op, a, b);
    }
    return 0;
}

2. 循环代替多层 if

#include <bits/stdc++.h>
using namespace std;
int cal(int x)
{
    bool flag = false;
    if (x < 0)
    {
        flag = true;
        x = -x;
    }
    for (int i = 10, j = 1;; i *= 10, j++)
        if (x < i)
            return j + flag;
}
void f(char op, int a, int b)
{
    int c;
    if (op == 'a')
    {
        c = a + b;
        op = '+';
    }
    else if (op == 'b')
    {
        c = a - b;
        op = '-';
    }
    else if (op == 'c')
    {
        c = a * b;
        op = '*';
    }
    cout << a << op << b << "=" << c << "\n";
    cout << cal(a) + cal(b) + cal(c) + 2 << "\n";
}
int main()
{
    int n;
    cin >> n;
    char op;     // 运算符
    int a, b;    // 两个运算数
    string temp; // 临时字符串
    for (int i = 1; i <= n; i++)
    {
        cin >> temp;
        if ('0' <= temp[0] && temp[0] <= '9')
        {
            a = 0;
            for (int j = 0; j < temp.size(); j++)
                a = a * 10 + (temp[j] - '0');
            cin >> b;
        }
        else
        {
            op = temp[0];
            cin >> a;
            cin >> b;
        }
        f(op, a, b);
    }
    return 0;
}

3. 数位分解计算位数（注意特判 0）

#include <bits/stdc++.h>
using namespace std;
int cal(int x)
{
    if (x == 0)
        return 1;
    int res = 0;
    if (x < 0)
    {
        res = 1;
        x = -x;
    }
    while (x > 0)
    {
        res++;
        x /= 10;
    }
    return res;
}
void f(char op, int a, int b)
{
    int c;
    if (op == 'a')
    {
        c = a + b;
        op = '+';
    }
    else if (op == 'b')
    {
        c = a - b;
        op = '-';
    }
    else if (op == 'c')
    {
        c = a * b;
        op = '*';
    }
    cout << a << op << b << "=" << c << "\n";
    cout << cal(a) + cal(b) + cal(c) + 2 << "\n";
}
int main()
{
    int n;
    cin >> n;
    char op;     // 运算符
    int a, b;    // 两个运算数
    string temp; // 临时字符串
    for (int i = 1; i <= n; i++)
    {
        cin >> temp;
        if ('0' <= temp[0] && temp[0] <= '9')
        {
            a = 0;
            for (int j = 0; j < temp.size(); j++)
                a = a * 10 + (temp[j] - '0');
            cin >> b;
        }
        else
        {
            op = temp[0];
            cin >> a;
            cin >> b;
        }
        f(op, a, b);
    }
    return 0;
}

4. 利用字符串流

#include <bits/stdc++.h>
using namespace std;
int n;
string s;
void f(char c, int a, int b)
{
    stringstream ss;
    if (c == 'a')
        ss << a << "+" << b << "=" << a + b << "\n";
    if (c == 'b')
        ss << a << "-" << b << "=" << a - b << "\n";
    if (c == 'c')
        ss << a << "*" << b << "=" << a * b << "\n";
    string s;
    getline(ss, s);
    cout << s << "\n";
    cout << s.length() << "\n";
}
int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> n;
    getline(cin, s);
    char c;
    int a, b;
    while (n--)
    {
        getline(cin, s);
        stringstream ss;
        ss << s;
        if ('0' <= s[0] && s[0] <= '9')
        {
            ss >> a >> b;
            f(c, a, b);
        }
        else
        {
            ss >> c >> a >> b;
            f(c, a, b);
        }
    }
    return 0;
}