實驗內容：計算字首表示式的值。
輸入說明：輸入一行不超過30個字元的字首表示式，只包含＋、－、＊、／以及運算數，不同物件之間用空格分隔。
輸出說明：輸出字首表示式的運算結果，精確到小數點後1位，或輸出錯誤資訊“ERROR“。
測試用例：
輸入 ｜ 輸出
＋ ＋ 2 ＊ 3 － 7 4 ／ 8 4 ｜ 13.0
／ －25 ＋ ＊ － 2 3 4 ／ 8 4 ｜ 12.5
／ 5 ＋ ＊ － 2 3 4 ／ 8 2 ｜ ERROR
＋10.23 ｜ 10.2

#include <stdio.h>
#include <stdlib.h>

#define MaxSize 30
 


typedef struct {
    char *arr;
    int size;
} *PList_3_7;

PList_3_7 initList_3_7();
void addList_3_7(PList_3_7 list, char c);
void printList_3_7(PList_3_7 list);
void clearList_3_7(PList_3_7 list);
void releaseList_3_7(PList_3_7 list);

float doCharArr2Float_3_7(char *arr, int startIndex, int size);
float
 
 doCal_3_7(char opt, float num1, float num2);

int main() {
    float n = test_3_7_0();
    if (n > -9999999) {
        printf("%.1f\n", n);
    }
    return 0;
}

float test_3_7_0() {
    float num = 0;
    PList_3_7 list = initList_3_7();
    char c;
    while (1) {
        c = getchar();
        if
 
 (c != ' ' && c != '\n') {
            addList_3_7(list, c);
        } else {
            if (list->size > 1) {
                if (list->arr[0] == '-' || list->arr[0] == '+') {
                    num = doCharArr2Float_3_7(list->arr, 1, list->size);
                    if (list->arr[0] == '-') {
                        num *= -1;
                    }
                } else {
                    num = doCharArr2Float_3_7(list->arr, 0, list->size);
                }
                break;
            } else if (list->size == 1) {
                if (list->arr[0] >= '0' && list->arr[0] <= '9') {
                    num = doCharArr2Float_3_7(list->arr, 0, list->size);
                    break;
                } else {
                    char opt = list->arr[0];
                    float num1 = test_3_7_0();
                    float num2 = test_3_7_0();
                    if (num1 <= -8999999 || num2 <= -8999999) {
                        num = -9999999;
                    } else {
                        num = doCal_3_7(opt, num1, num2);
                    }
                    break;
                }
            }
            clearList_3_7(list);
        }
        if (c == '\n') {
            break;
        }
    }
    return num;
}

PList_3_7 initList_3_7() {
    PList_3_7 list = (PList_3_7) malloc(sizeof(PList_3_7));
    list->arr = (char *) malloc(sizeof(char) * MaxSize);
    list->size = 0;
    return list;
}

void addList_3_7(PList_3_7 list, char c) {
    if (list->size < MaxSize) {
        list->arr[list->size] = c;
        list->size ++;
    }
}

void printList_3_7(PList_3_7 list) {
    for (int i = 0; i < list->size; i++) {
        printf("%c", list->arr[i]);
    }
    printf("\n");
}

void clearList_3_7(PList_3_7 list) {
    list->size = 0;
}

void releaseList_3_7(PList_3_7 list) {
    free(list->arr);
    free(list);
}

float doCharArr2Float_3_7(char *arr, int startIndex, int size) {
    int num1 = 0;
    float num2 = 0;
    int i = startIndex;
    while (i < size) {
        if (arr[i] == '.') {
            i++;
            break;
        }
        num1 = num1 * 10 + (arr[i] - '0');
        i++;
    }
    float j = 10.0;
    while (i < size) {
        num2 += (arr[i] - '0') / j;
        j *= 10;
        i++;
    }
    return num1 + num2;
}

float doCal_3_7(char opt, float num1, float num2) {
    float num = 0;
    switch (opt) {
        case '+' :
            num = num1 + num2;
            break;
        case '-' :
            num = num1 - num2;
            break;
        case '*' :
            num = num1 * num2;
            break;
        case '/' :
            if (num2 > -0.000001 && num2 < 0.000001) {
                printf("ERROR\n");
                num = -9999999;
            } else {
                num = num1 / num2;
            }
    }
    return num;
}