C++考试编程题求助：计算输入五个浮点数中的偶数和

题目要求：编写完整程序，允许用户输入五个浮点数，计算其中偶数的和。例如输入12、15、3、5、10时，应输出22（12和10为偶数，和为22），且输入值均大于0。

现有代码 #

#include <iostream>
using namespace std;

int main()
{
    float numOne = 0;
    float numTwo = 0;
    float numThree = 0;
    float numFour = 0;
    float numFive = 0;
    float evenSum = 0;

    cout << "Please enter the first number";
    cin >> numOne;
    cout << "Please enter the second number";
    cin >> numTwo;
    cout << "Please enter the third number";
    cin >> numThree;
    cout << "Please enter the fourth number";
    cin >> numFour;
    cout << "Please enter the fifth number";
    cin >> numFive;

    return 0;
}

完整解决方案代码 #

以下代码实现了输入验证、偶数判断及求和逻辑，同时用数组优化了变量管理：

#include <iostream>
#include <cmath> // 用于计算浮点数余数的fmod函数
using namespace std;

int main()
{
    float nums[5];
    float evenSum = 0.0;

    // 循环处理5次输入
    for (int i = 0; i < 5; ++i) {
        cout << "Please enter number " << i + 1 << ": ";
        cin >> nums[i];
        
        // 强制输入大于0的数，不合法则重新输入
        while (nums[i] <= 0) {
            cout << "Input must be greater than 0. Please re-enter: ";
            cin >> nums[i];
        }

        // 判断浮点数是否为偶数：除以2余数为0
        if (fmod(nums[i], 2.0) == 0.0) {
            evenSum += nums[i];
        }
    }

    cout << "Sum of even numbers: " << evenSum << endl;

    return 0;
}

关键逻辑说明 #

• 输入验证：通过while循环拦截小于等于0的输入，确保符合题目要求。
• 偶数判断：使用fmod函数计算浮点数与2的余数，余数为0则判定为偶数（适配浮点数场景，如12.0会被识别为偶数，12.5则不会）。
• 数组优化：用数组替代单独变量，简化代码结构，后续若需调整输入数量只需修改循环次数即可。

初学者友好版（单独变量写法） #

如果更习惯用单独变量管理输入，可使用以下版本：

#include <iostream>
#include <cmath>
using namespace std;

int main()
{
    float numOne = 0, numTwo = 0, numThree = 0, numFour = 0, numFive = 0;
    float evenSum = 0.0;

    // 第一个数输入与验证
    cout << "Please enter the first number: ";
    cin >> numOne;
    while (numOne <= 0) {
        cout << "Input must be greater than 0. Please re-enter: ";
        cin >> numOne;
    }
    if (fmod(numOne, 2.0) == 0.0) evenSum += numOne;

    // 第二个数输入与验证
    cout << "Please enter the second number: ";
    cin >> numTwo;
    while (numTwo <= 0) {
        cout << "Input must be greater than 0. Please re-enter: ";
        cin >> numTwo;
    }
    if (fmod(numTwo, 2.0) == 0.0) evenSum += numTwo;

    // 第三个数输入与验证
    cout << "Please enter the third number: ";
    cin >> numThree;
    while (numThree <= 0) {
        cout << "Input must be greater than 0. Please re-enter: ";
        cin >> numThree;
    }
    if (fmod(numThree, 2.0) == 0.0) evenSum += numThree;

    // 第四个数输入与验证
    cout << "Please enter the fourth number: ";
    cin >> numFour;
    while (numFour <= 0) {
        cout << "Input must be greater than 0. Please re-enter: ";
        cin >> numFour;
    }
    if (fmod(numFour, 2.0) == 0.0) evenSum += numFour;

    // 第五个数输入与验证
    cout << "Please enter the fifth number: ";
    cin >> numFive;
    while (numFive <= 0) {
        cout << "Input must be greater than 0. Please re-enter: ";
        cin >> numFive;
    }
    if (fmod(numFive, 2.0) == 0.0) evenSum += numFive;

    cout << "Sum of even numbers: " << evenSum << endl;

    return 0;
}

内容的提问来源于stack exchange，提问作者Ethan Dentner