1024 科学计数法 (20 分)

+1.23400E-03

0.00123400

-1.2E+10

-12000000000

// 1024 科学计数法 (20 分).cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//

#include <iostream>
#include <string>
using namespace std;
//输出有效数字
void print(string s, int point_index, bool point) {
    bool E_flag = false;
    for (int i = 0; i < s.size(); i++) {
        if (s[i] == 'E')
            E_flag = true;
        if (point && point_index == i)
            cout << ".";
        if (!E_flag && s[i] >= '0' && s[i] <= '9')
            cout << s[i];
    }
}

//判断幂的符号以及数值
int judge(string s) {
    bool E_flag = false;
    int res = 0;
    int tmp = 1;
    for (int i = s.length() - 1; i > 0; i--) {
        if (s[i] == 'E')
            E_flag = true;
        if (!E_flag && s[i] >= '0' && s[i] <= '9') {
            res += (s[i] - '0') * tmp;
            tmp *= 10;
        }
        else if (!E_flag && s[i] == '-') {
            res *= -1;
        }
    }
    return res;
}
int main(){
    string input;
    cin >> input;
    int flag;
    int num = judge(input);
    //得到E的位置
    int E_index;
    for (int i = 0; i < input.size(); i++) {
        if (input[i] == 'E')
            E_index = i;
    }
    int zero_count = 0;
    for (int i = 0; i < E_index; i++) {
        if (input[i] == '0')
            zero_count++;
    }
    //如果数值为0
    if (zero_count + 1 >= E_index) {
        cout << "0";
        return 0;
    }
    //如果指数为0
    else if (num == 0) {
        for (int i = 0; i < E_index; i++) {
            if(input[i] != '+')
                cout << input[i];
        }
    }
    else {
        if (input[0] == '-')
            cout << "-";
        if (num < 0) {
            cout << "0.";
            for (int i = 0; i < (-1 * num) - 1; i++)
                cout << "0";
            print(input, 0, false);
        }
        if (num > 0) {
            if (num >= E_index - 3) {
                print(input , 0,false);
                for (int i = 0; i < num - (E_index - 3); i++)
                    cout << "0";
            }
            else {
                print(input, num + 3, true);
            }

        }
    }
}