C:评估队列中的表达式不起作用 [英] C: Evaluating Expression in a queue not working

问题描述

我使用链接列表创建了一个队列，该队列采用格式为 1 + 3 + 5 = 或 1-3 + 2-4 = 的字符串，但以下内容应该执行给定符号并产生答案的代码无法正常工作，例如，如果我传递了类似 66-31-21-21 + 43 = 的字符串，则答案是 -47 而不是 57 .有人可以帮我解决问题，还是指出我做错了什么.

I have created a queue using linked list that takes a string in the format 1 + 3 + 5 =or 1-3+2-4 = but the following code which is supposed to do the calculation given the sign and produce the answer is not working right for example if I passed a string like 66 - 31 - 21 + 43 = is passed the answer turns out to be -47 instead of 57. Can someone help me solve it or point to what I'm doing wrong.

void printQueue(struct node* head)
{
    struct node* temp;
    char *token, *del=" ";
    int total = 0;

    while (head != NULL)
    {

        token = strtok(head->data, del);
        while (token != NULL) {
            int a = strcmp(token, "+");
            int b = strcmp(token, "-");
            if (a == 0)
            {
                printf("+");
                total = total + *token;
            }
            else if (b == 0) {
                printf("+");
                total = total - *token;
            }

            printf("%s ", token);
            token = strtok(NULL, del);
        }

        printf(" %d\n",subtraction);
        head = head->next;
    }
}

推荐答案

您的代码忽略了数字，将'+'和'-'的字符代码相加字符代替.数字 -47 是-45-45 + 43的计算结果:45是破折号的字符代码；加号的字符代码为43.

Your code is ignoring the numbers, adding up character codes of '+' and '-' characters instead. The number -47 is the result of computing -45-45+43: 45 is the character code for the dash; 43 is the character code for the plus.

为了正常工作，请对您的代码进行以下更改:

In order to work properly, make these changes to your code:

• 添加 int 类型的 sign 变量，其初始值为 1
• 看到加号时，请将 sign 设置为 1
• 看到减号时，请将 sign 设置为 -1
• 当您看到既不是加号也不是减号的令牌时，请将其转换为 int val (例如，通过调用 atoi )，然后添加 val *签名到运行总计.

• Add a sign variable of int type, with the initial value of 1
• When you see a plus sign, set the sign to 1
• When you see a minus sign, set the sign to -1
• When you see a token that is neither a plus nor minus, convert it to an int val (e.g. by calling atoi), and add val * sign to the running total.

此更改将使您的代码适用于有效的表达式，但对于某些无效的表达式也不会失败.例如，将采用诸如 1 2 3 之类的表达式"，就好像它是 1 + 2 + 3 一样，依此类推.

This change will make your code work for valid expressions, but it would not fail for some invalid ones. For example, it would take "expressions" such as 1 2 3 as if it were 1+2+3, and so on.

这篇关于C:评估队列中的表达式不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！