Question

我目前正在尝试编写一个程序，该程序需要三个整数，并对它们进行排序（从最小到最大），然后将它们与键入的原始顺序一起输出。该程序有很多错误，例如，当我输入“ 4 7 9”时，程序会将其分类为“ 4 9 9”。但是，如果我执行“ 65 32 11”，则程序会将其正确排序为“ 11 32 65”。我只是想知道我的代码出了什么问题，以及如何改进它以及将来的项目。

cout << "Please input 3 integers with a space inbetween them.\n";
int v1;
int v2;
int v3;

int smallest = 0;
int middle = 0;
int largest = 0;

cin >> v1 >> v2 >> v3;

    if (v1 <= v2 && v1 <= v3) {
        smallest = v1;
        if (v2 <= v3) {
            middle = v2;
            largest = v3;
        }
        else
            largest = v2;
        middle = v3;
    }

    else if (v2 <= v1 && v2 <= v3) {
        smallest = v2;
        if (v1 <= v3) {
            middle = v1;
            largest = v3;
        }
        else
            largest = v1;
        middle = v3;
    }
    else {
        smallest = v3;
        if (v1 <= v2) {
            middle = v1;
            largest = v2;
        }
        else
            largest = v1;
        middle = v2;
    }

cout << "Input values: " << v1 << ", " << v2 << ", " << v3 << '\n';
cout << "Sorted values: " << smallest << ", " << middle << ", " << largest << '\n';

keep_window_open();
}

Answer 1

cout << "Please input 3 integers with a space inbetween them.\n";
int v1;
int v2;
int v3;

int smallest = 0;
int middle = 0;
int largest = 0;

cin >> v1 >> v2 >> v3;

    if (v1 <= v2 && v1 <= v3) {
        smallest = v1;
        if (v2 <= v3) {
            middle = v2;
            largest = v3;
        }

其他部分缺少{}

        else{
            largest = v2;
            middle = v3;
        }
    }

    else if (v2 <= v1 && v2 <= v3) {
        smallest = v2;
        if (v1 <= v3) {
            middle = v1;
            largest = v3;
        }

其他部分缺少{}

        else{
            largest = v1;
            middle = v3;
            }
    }
    else {
        smallest = v3;
        if (v1 <= v2) {
            middle = v1;
            largest = v2;
        }

其他部分缺少{}

        else{
            largest = v1;
            middle = v2;
            }
    }

cout << "Input values: " << v1 << ", " << v2 << ", " << v3 << '\n';
cout << "Sorted values: " << smallest << ", " << middle << ", " << largest << '\n';

keep_window_open();
}

如果您查看所有if else的else部分，就会发现{}丢失了您的最大和中间价值。

更多信息...

if(condition)     /* if statement with condition */
    statement;    /* executes if the if condition is true even without the {} */
else              /* else statement when if condition is false */
    statement;    /* executes when else is true without the {} */
    statement;    /* Visually misguided but execution does not depend
                     upon the else statement, this line always gets executed,
                     compiler only looks at the first line after if else without {} */

Answer 2

首先出现在我身上的是您的else语句。在C / C ++中，不带括号的else语句将在条件满足时执行下一条语句。如果不存在大括号，它将不会执行多个语句。这在代码中是有问题的，因为无论您的第二级middle语句如何，您的if值都会被覆盖。作为参考，可以在SO的软件工程页面上查看discussion。

替换

if (v1 <= v2 && v1 <= v3) {
    smallest = v1;
    if (v2 <= v3) {
        middle = v2;
        largest = v3;
    }
    else
        largest = v2;
    middle = v3;
}

使用

if (v1 <= v2 && v1 <= v3) {
    smallest = v1;
    if (v2 <= v3) {
        middle = v2;
        largest = v3;
    }
    else
    {
        largest = v2;
        middle = v3;
    }

作为旁注，如果您要考虑更多位数，则应考虑实现Radix排序。单击此处获取Radix Sorting Algorithm Tutorial

程序主要使用if和else语句未正确执行

2 个答案: