逆波兰表达式（后缀表达式）：将正常表达式（中缀表达式）转化为代码理解的类型
以下是计算逆波兰表达式的结果代码：

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#define INIT_SIZE 10240
#define ADD_SIZE 10

typedef struct {
char* base;
char* top;
int Stacksize;
} Stack;

void Init_stack(Stack* s) //此次为初始化栈

void Push_stack(Stack* s, char e) //此处为入栈

char Pop_stack(Stack* s) //此处为出栈

int Stacklen(Stack s) //计算栈的当前大小

void Destroy_stack(Stack* s) //销毁栈

void Calculate(Stack* s)
{
char c;
char str[10];
double d, e;
int i = 0;
printf("请输入数据，用空格隔开，；以#代表结束\n");
scanf(" %c", &c); // 注意前面的空格，用于跳过空白字符

while (c != '#') {
    while (isdigit(c) || c == '.') 
   {
        str[i++] = c;
        if (i >= 10)
        {
            printf("输入单个数据过大！\n");
            return;
        }
        scanf(" %c", &c);
    }
    str[i] = '\0';
    d = atof(str);
    Push_stack(s, d);
    i = 0;

    switch (c) 
    {
        case '+':
            e = Pop_stack(s);
            d = Pop_stack(s);
            Push_stack(s, d + e);
            break;
        case '-':
            e = Pop_stack(s);
            d = Pop_stack(s);
            Push_stack(s, d - e);
            break;
        case '*':
            e = Pop_stack(s);
            d = Pop_stack(s);
            Push_stack(s, d * e);
            break;
        case '/':
            e = Pop_stack(s);
            d = Pop_stack(s);
            if (e != 0) 
            {
                Push_stack(s, d / e);
            } else 
            {
                printf("出错，除数为0\n");
                return;
            }
            break;
        default:
            break;
    }
    scanf(" %c", &c);
}
d = Pop_stack(s);
printf("结果为：%f\n", d);

}

接下来是中缀表达式转化为后缀表达式的代码

void Calculate(Stack* s)
{
char c;
char str[10];
double d, e;
int i = 0;

printf("请输入数据，用空格隔开，以#代表结束\n");
scanf(" %c", &c);

while (c != '#')

{
// 读取数字部分
while (isdigit(c) || c == '.')
{
str[i++] = c;
if (i >= 10)
{
printf("输入单个数据过大！\n");
return;
}
scanf("%c", &c);
}
str = '\0';
if (i > 0)
{ // 有效数字才转换
d = atof(str);
Push_stack(s, d);
}
i = 0;

    // 处理运算符
    switch (c) 
    {
    case '+':
        e = Pop_stack(s);
        d = Pop_stack(s);
        if (d == -1 || e == -1) return;
        Push_stack(s, d + e);
        break;
    case '-':
        e = Pop_stack(s);
        d = Pop_stack(s);
        if (d == -1 || e == -1) return;
        Push_stack(s, d - e);
        break;
    case '*':
        e = Pop_stack(s);
        d = Pop_stack(s);
        if (d == -1 || e == -1) return;
        Push_stack(s, d * e);
        break;
    case '/':
        e = Pop_stack(s);
        d = Pop_stack(s);
        if (d == -1 || e == -1) return;
        if (e != 0) 
        {
            Push_stack(s, d / e);
        }
        else 
        {
            printf("出错，除数为0\n");
            return;
        }
        break;
    default:
        break;
    }
    scanf(" %c", &c);
}
d = Pop_stack(s);
if (d != -1) 
 {
    printf("结果为：%f\n", d);
}

}
//用于比较运算符优先级
int precedence(char op)
{
if (op == '+' op == '-') return 1;
if (op == '*' op == '/') return 2;
return 0; // 其他字符（如 '('）
}

char* Change_order(Stack* s)
{
char c;
char output[1024]; // 用于存储后缀表达式
int index = 0; // output 数组的索引

printf("请输入表达式，以 # 结束：\n");
char input[1025];
fgets(input, sizeof(input), stdin);
input[strcspn(input, "\n")] = 0; // 去除换行符

for (int i = 0; input[i] != '#'; i++) 
{
    c = input[i];
    if (isdigit(c) || c == '.') 
    {
        while (isdigit(input[i]) || input[i] == '.') 
        {
            output[index++] = input[i++];
        }
        output[index++] = ' '; // 数字后加空格作为分隔符
        i--; // 因为循环中 i 会自增，所以这里要减一
    }
    else if (c == '(') 
    {
        Push_stack(s, c);
    }
    else if (c == ')') 
    {
        while (s->top != s->base && *(s->top - 1) != '(') 
        {
            output[index++] = Pop_stack(s);
            output[index++] = ' ';
        }
        Pop_stack(s); // 弹出 '('
    }
    else if (c == '*' || c == '/' || c == '+' || c == '-') 
    {
        while (s->top != s->base && precedence(c) <= precedence(*(s->top - 1))) 
        {
            output[index++] = Pop_stack(s);
            output[index++] = ' ';
        }
        Push_stack(s, c);
    }
    else 
    {
        printf("输入未定义字符，请重新输入！\n");
        return;
    }
}

// 将栈中剩余操作符弹出到 output 数组
while (s->top != s->base) 
{
    output[index++] = Pop_stack(s);
    output[index++] = ' ';
}

output[index] = '\0'; // 添加字符串结束符

printf("后缀表达式为：%s\n", output);
return output;

}

int main()
{
Stack s;
char* myarr;
Init_stack(&s);
myarr = Change_order(&s);
Destroy_stack(&s);
return 0;
}