我正在嘗試從書中做一個練習：編程——使用 C++ 的原則和實踐（第二版）

Question

編寫一個程序，提示用戶輸入三個整數值，然后以逗號分隔的數字順序輸出這些值。 因此，如果用戶輸入值 10 4 6，則輸出應為 4, 6, 10。如果兩個值相同，則應將它們排列在一起。 因此，輸入 4 5 4 應該給出 4, 4, 5。

int main()
{
    cout << "Please enter three integer values seperated by a space (press 'enter' when done):\n";   //prompt
    int val1, val2, val3 = 0;
    cin >> val1 >> val2 >> val3;
    if (val1 <= val2 && val2 <= val3)
    {
        cout << val1 << ", " << val2 << ", " << val3 << "\n";
    }
    if (val1 >= val2 && val2 >= val3)
    {
        cout << val3 << ", " << val2 << ", " << val1 << "\n";
    }
    if (val2 <= val3 && val3 <= val1)
    {
        cout << val2 << ", " << val3 << ", " << val1 << "\n";
    }
    if (val3 <= val1 && val1 <= val2)
    {
        cout << val3 << ", " << val1 << ", " << val2 << "\n";
    }
    if (val1 <= val3 && val3 <= val2)
    {
        cout << val1 << ", " << val3 << ", " << val2 << "\n";
    }
    if (val2 <= val1 && val1 <= val3)
    {
        cout << val2 << ", " << val1 << ", " << val3 << "\n";
    }
}

該程序適用於所有值。 我遇到的唯一問題是：當我輸入諸如2 2 3 之類的重復值時，我會收到兩次輸出 2, 2, 3 而不是一次。 對不起，我沒有評論任何一行。 這似乎不言自明，我不知道我會評論什么。

Answer 1

保持你的邏輯，你應該使用else if ：

if (val1 <= val2 && val2 <= val3)
{
    cout << val1 << ", " << val2 << ", " << val3 << "\n";
}
else if (val1 >= val2 && val2 >= val3)
{
    cout << val3 << ", " << val2 << ", " << val1 << "\n";
}
else if (val2 <= val3 && val3 <= val1)
{
    cout << val2 << ", " << val3 << ", " << val1 << "\n";
}
else if (val3 <= val1 && val1 <= val2)
{
    cout << val3 << ", " << val1 << ", " << val2 << "\n";
}
else if (val1 <= val3 && val3 <= val2)
{
    cout << val1 << ", " << val3 << ", " << val2 << "\n";
}
else if (val2 <= val1 && val1 <= val3)
{
    cout << val2 << ", " << val1 << ", " << val3 << "\n";
}

但可以簡化為

int values[3];

for (int& value : values)
    std::cin >> value;
std::sort(std::begin(values), std::end(values));
const char* sep = "";
for (int value : values) {
    std::cout << sep << value;
    sep = ", ";
}
std::cout << std::endl;