C language: stack exercise-postfix evaluation

C language: stack exercise-postfix evaluation

//
// Created by Michael on 2020/4/5.
//
#include <stdio.h>

#define MAXSIZE 100
typedef struct Stack{
    
    
    double value[MAXSIZE];
    int top;
}Stack;


void Init_Stack(Stack *S);
void Push_data(Stack *S, double d);
double if_data(Stack *S,char input[]);
double Calculate(Stack *S,double left,double right,char c);


int main()
{
    
    
    //14 3 20 5 /* 8 -+
    Stack S;
    double result;
    char input[100];
    while (1)
    {
    
    
        char flag = 0;
        Init_Stack(&S);

        printf("请输入后缀式:\n");
        gets(input);
        result = if_data(&S,input);
        printf("=%.2lf\n",result);
        printf("是否继续输入'y'or''n:");
        e:scanf("%c",&flag);
        fflush(stdin);
        if (flag == 'n' || flag == 'y')
        {
    
    
            if (flag == 'n')
            {
    
    
                printf("运行结束!\n");
                break;
            }

        }
        else
        {
    
    
            printf("输入有误,请输入'y'or'n':");
            goto e;
        }

        fflush(stdin);
    }

    return 0;
}

void Init_Stack(Stack *S) //初始化栈
{
    
    
    S->top = -1;
}

void Push_data(Stack *S, double d) //进栈
{
    
    
    S->top++;
    S->value[S->top] = d;
    // printf("%.0lf  ",S->value[S->top]);
}

double Calculate(Stack *S, double left, double right, char c) //运算
{
    
    
    double equal = 0;
    switch (c)
    {
    
    
        case '+':
            equal = left + right;
            break;
        case '-':
            equal = left - right;
            break;
        case '*':
            equal = left * right;
            break;
        case '/':
            equal = left / right;
            break;
        default:
            break;
    }
    S->top--;
    S->value[S->top]=equal;
    // printf("%.2lf  %.2lf /",left,right);
    return equal;
}

double if_data(Stack *S,char input[])//判断是否是数字
{
    
    
    int i = 0;

    double n = 0;
    double temp = 0;
    for(i=0;input[i]!='\0';i++)
    {
    
    
        if (input[i]<='9' && input[i]>='0')
        {
    
    
            temp = input[i]-'0';
            while (input[i+1]!='\0')
            {
    
    
                if (input[i+1]<='9' && input[i+1]>='0')
                {
    
    
                    temp = temp*10 + (input[i+1]-'0');
                    i++;
                }
                else
                    break;
            }
            Push_data(S,temp);
        }
        else if (input[i]=='+' || input[i]=='-' || input[i]=='*' || input[i]=='/' )
        {
    
    
            //printf("%c",input[i]);
            n=Calculate(S,S->value[S->top-1],S->value[S->top],input[i]);
        }

    }
    return n;
}