HW3_poland_notation

#include <cstdio>
#include <cstdlib>
#include <cmath>

int ch(char a)
{
    if (a == '^')
        return 4;
    if (a == '*' || a == '/')
        return 3;
    if (a == '+' || a == '-')
        return 2;
    if (a == '(' || a == ')')
        return 1;
    return 0;
}

int nin(char a, char* b)
{
    for (int i = 0; i < 7; i++)
    {
        if (a == b[i])
            return 0;
    }
    return 1;
}

int sr(char a, char b)
{
    a = ch(a);
    b = ch(b);
    return a >= b;
}

int pr(char a, char b, char c)
{
    if (c == '+')
        return (a + b);
    if (c == '-')
        return (a - b);
    if (c == '*')
        return (a * b);
    if (c == '/')
        return (a / b);
    return pow(a, b);
}

int main()
{
    int n = 0, t = -1, k = -1;
    char* q = "()+-*/^";
    scanf("%d", &n);
    char* arr = (char*)malloc(n);
    char* stack = (char*)malloc(n);
    char* ans = (char*)malloc(n);
    scanf("%s", arr);
    for (int i = 0; i < n; i++)
    {
        if (nin(arr[i], q))
        {
            printf("%c ", arr[i]);
            k++;
            ans[k] = arr[i];
        }
        else if (t == -1)
        {
            t++;
            stack[t] = arr[i];
        }
        else
        {
            while (arr[i] != '(' && sr(stack[t], arr[i]) && t > 0)
            {
                if (stack[t] != '(')
                {
                    k++;
                    ans[k] = stack[t];
                    printf("%c ", stack[t]);
                    t--;
                }
                else
                {
                    t--;
                    break;
                }
            }
            if (arr[i] != ')')
            {
                t++;
                stack[t] = arr[i];
            }
        }
    }
    while (t != -1)
    {
        if (stack[t] != '(')
        {
            k++;
            ans[k] = stack[t];
            printf("%c ", stack[t]);
            t--;
        }
    }
    for (int i = 0; i <= k; i++)
    {
        if (nin(ans[i], q))
        {
            t++;
            stack[t] = ans[i] - 48;
        }
        else
        {
            t--;
            stack[t] = pr(stack[t], stack[t + 1], ans[i]);
        }
    }
    printf("\n%d\n", stack[t]);
    return 0;
}