题解 | #四则运算#

#include<stdio.h>
#include<string.h>
int compute(int num1, int num2, char symbol)//主运算函数
{
    int ans;
    switch (symbol)
    {
    case '+':
        ans = num1 + num2;
        break;
    case '-':
        ans = num1 - num2;
        break;
    case '*':
        ans = num1 * num2;
        break;
    case '/':
        ans = num1 / num2;
        break;
    }
    return ans;
}

int main(void)
{
    char str[1000] = { 0 };
    char symbol_stack[1000] = { 0 };//符号栈
    int number_stack[1000] = { 0 };//数字栈
    int s_size = 0, n_size = 0;
    int i = 0;
    int num1, num2;
    scanf("%[^\n]", &str);
    int len = strlen(str);
    for (i = 0; i < len; i++)//遍历字符串
    {
        if (str[i] == '(' || str[i] == '[' || str[i] == '{')
        {
            symbol_stack[s_size++] = str[i];//左括号直接压入符号栈
        }
        if (str[i] == '-')
        {
            //先判断是符号还是减号
            if (i == 0 || str[i - 1] == '(' || str[i - 1] == '[' || str[i - 1] == '{') // 代表符号
            {
                int temp = 0;
                i++;
                while (str[i] >= '0' && str[i] <= '9')
                {
                    temp = 10 * temp + str[i] - '0';
                    i++;
                }
                number_stack[n_size++] = 0 - temp;
            }
            else//代表减号
            {
                while (s_size > 0 && (symbol_stack[s_size - 1] == '-' || symbol_stack[s_size - 1] == '*' || symbol_stack[s_size - 1] == '/'))
                {
                    num2 = number_stack[--n_size];
                    num1 = number_stack[--n_size];
                    number_stack[n_size++] = compute(num1, num2, symbol_stack[--s_size]);
                }
                symbol_stack[s_size++] = '-';
            }
        }
        if (str[i] == '+')
        {
            //先判断是符号还是加号
            if (i == 0 || str[i - 1] == '(' || str[i - 1] == '[' || str[i - 1] == '{') // 代表符号
            {

            }
            else//代表加号
            {
                while (s_size > 0 && (symbol_stack[s_size - 1] == '-' || symbol_stack[s_size - 1] == '*' || symbol_stack[s_size - 1] == '/'))
                {
                    num2 = number_stack[--n_size];
                    num1 = number_stack[--n_size];
                    number_stack[n_size++] = compute(num1, num2, symbol_stack[--s_size]);
                }
                symbol_stack[s_size++] = '+';
            }
        }
        if (str[i] == '*')
        {
            while (s_size > 0 && (symbol_stack[s_size - 1] == '/'))
            {
                num2 = number_stack[--n_size];
                num1 = number_stack[--n_size];
                number_stack[n_size++] = compute(num1, num2, symbol_stack[--s_size]);
            }
            symbol_stack[s_size++] = '*';
        }
        if (str[i] == '/')
        {
            while (s_size > 0 && (symbol_stack[s_size - 1] == '*' || symbol_stack[s_size - 1] == '/'))
            {
                num2 = number_stack[--n_size];
                num1 = number_stack[--n_size];
                number_stack[n_size++] = compute(num1, num2, symbol_stack[--s_size]);
            }
            symbol_stack[s_size++] = '/';
        }
        if (str[i] >= '0' && str[i] <= '9')
        {
            int temp = 0;
            while (str[i] >= '0' && str[i] <= '9')
            {
                temp = temp * 10 + str[i] - '0';
                i++;
            }
            if (!(str[i] >= '0' && str[i] <= '9'))
            {
                i--;
            }
            number_stack[n_size++] = temp;
        }
        if (str[i] == ')')
        {
            while (symbol_stack[s_size - 1] != '(')
            {
                num2 = number_stack[--n_size];
                num1 = number_stack[--n_size];
                number_stack[n_size++] = compute(num1, num2, symbol_stack[--s_size]);
            }
            s_size--;
        }
        if (str[i] == ']')
        {
            while (symbol_stack[s_size - 1] != '[')
            {
                num2 = number_stack[--n_size];
                num1 = number_stack[--n_size];
                number_stack[n_size++] = compute(num1, num2, symbol_stack[--s_size]);
            }
            s_size--;
        }
        if (str[i] == '}')
        {
            while (symbol_stack[s_size - 1] != '{')
            {
                num2 = number_stack[--n_size];
                num1 = number_stack[--n_size];
                number_stack[n_size++] = compute(num1, num2, symbol_stack[--s_size]);
            }
            s_size--;
        }

    }
    while (s_size > 0)
    {
        num2 = number_stack[--n_size];
        num1 = number_stack[--n_size];
        number_stack[n_size++] = compute(num1, num2, symbol_stack[--s_size]);
    }
    printf("%d", number_stack[--n_size]);
    return 0;
}