后缀表达式求解

思路： 根据输入的字符串 遇到数字 入栈 ，遇到运算符弹出两个数字计算，计算结果入栈，最后栈中剩余的数字就是最终结果。

代码示例：

//后缀表达式求解
void Postfix(char str[], Stack S)
{
    int i = 0, t1, t2;
    while (str[i] != '\0')
    {
        //数字入栈
        while (isdigit(str[i]))
            Push((str[i++]-48), S);
        //操作符出栈2个数，结果入栈
        t1 = Top(S);
        Pop(S);
        t2 = Top(S);
        Pop(S);
        switch (str[i])
        {
        case '+':
            Push(t1 + t2, S);
            break;
        case '-':
            Push(t1 - t2, S);
            break;
        case '*':
            Push(t1 * t2, S);
            break;
        case '/':
            Push(t1 / t2, S);
            break;
        default:
            printf("error");
            break;
        }
        i++;
    }
    printf("%d",Top(S));
}

完整程序：

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
//栈的定义
struct Node
{
    int Capacity;   //容量
    int TopOfStack; //栈顶
    int *Array;
} Node;
typedef struct Node *Stack, *PtrNode;
//创建栈
Stack CreatStack(int Max)
{
    Stack S;
    S = (PtrNode)malloc(sizeof(struct Node));
    if (S == NULL)
        printf("create stack error");
    S->Array = (int *)malloc(Max * sizeof(int));
    if (S->Array == NULL)
        printf("create stack error");
    S->Capacity = Max;
    S->TopOfStack = -1;
    return S;
}
int IsFull(Stack S)
{
    return S->TopOfStack == S->Capacity - 1;
}
int IsEmpty(Stack S)
{
    return S->TopOfStack == -1;
}
void Push(char x, Stack S)
{
    if (IsFull(S))
        printf("stack is full");
    else
    {
        S->TopOfStack = S->TopOfStack + 1;
        S->Array[S->TopOfStack] = x;
    }
    //    S->Array[++S->TopOfStack] = x;
}
void Pop(Stack S)
{
    if (IsEmpty(S))
        printf("stack is empty");
    else
        S->TopOfStack--;
}
char Top(Stack S)
{
    if (IsEmpty(S))
        printf("stack is empty");
    else
        return S->Array[S->TopOfStack];
}
//后缀表达式求解
void Postfix(char str[], Stack S)
{
    int i = 0, t1, t2;
    while (str[i] != '\0')
    {
        //数字入栈
        while (isdigit(str[i]))
            Push((str[i++]-48), S);
        //操作符出栈2个数，结果入栈
        t1 = Top(S);
        Pop(S);
        t2 = Top(S);
        Pop(S);
        switch (str[i])
        {
        case '+':
            Push(t1 + t2, S);
            break;
        case '-':
            Push(t1 - t2, S);
            break;
        case '*':
            Push(t1 * t2, S);
            break;
        case '/':
            Push(t1 / t2, S);
            break;
        default:
            printf("error");
            break;
        }
        i++;
    }
    printf("%d",Top(S));
}
int main()
{
    char str[100];
    printf("please input postfix expression\n");
    scanf("%s", str);
    int len = strlen(str);
    Stack S;
    S = CreatStack(len+1);
    Postfix(str, S);
}