用栈实现简单的四则运算

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#include<stdio.h>#include<stdlib.h>#define OK 10000#define ERROR 10001struct node{int data;struct node *next;};typedef struct node Node;struct stack{Node *top;int count;};typedef struct stack Stack; int InitStack(Stack *S){S->top = NULL;S->count = 0;    return OK;}int EmptyStack(Stack *S){return (S->count == 0) ? OK : ERROR;}int Push(Stack *S,int e){    Node *p = (Node *)malloc(sizeof(Node));    if(NULL == p)    {        return ERROR;    }    p->data = e;    p->next = S->top;    S->top = p;    S->count++;        return OK;}int GetTop(Stack *S){    if(NULL == S->top)    {        return ERROR;    }    return (S->top->data);}int Priority(char s){switch(s){case'(':return 3;case'*':case'/':return 2;case'+':case'-':return 1;default:return 0;}}int Pop(Stack *S){int e;if(NULL == S->top){        return ERROR;    }    Node *p = S->top;    e = p->data;    S->top = p->next;    free(p);    S->count--;return e;}int main(){Stack num, opt;char str[100] ={0};int i = 0,tmp = 0,j;if (InitStack(&num) !=OK || InitStack(&opt) !=OK){printf("Init Failure!\n");exit(1);}printf("Please Input Operator:\n");scanf("%s",str);while(str[i] !='\0' || EmptyStack(&opt) !=OK){if (str[i] >= '0' && str[i] <='9'){tmp = tmp * 10 + str[i] - '0';i++;if (str[i] < '0' || str[i] >'9'){Push(&num,tmp);tmp = 0;}}else{if ((EmptyStack(&opt) ==OK) || (GetTop(&opt)=='(' && str[i] !=')')|| //进栈不运算(Priority(str[i])>Priority(GetTop(&opt)))){Push(&opt,str[i]);i++;continue;}if (GetTop(&opt)=='(' && str[i] ==')')  //出栈不运算{Pop(&opt);i++;continue;}if ((str[i]=='\0' && EmptyStack(&opt) !=OK) || (str[i]==')' && GetTop(&opt) !='(')||  //出栈运算(Priority(str[i])<=Priority(GetTop(&opt)))){switch(Pop(&opt)){case '+':Push(&num,Pop(&num)+Pop(&num));break;case '-':j = Pop(&num);Push(&num,Pop(&num)-j);break;case '*':Push(&num,Pop(&num)*Pop(&num));break;case '/':j = Pop(&num);Push(&num,Pop(&num)/j);break;}continue;}}}printf("The result is :%d\n",Pop(&num));return 0;}

优先级高于栈顶才能进栈

遇到右括号，栈顶出来，左右括号消失

优先级小于等于栈顶，栈顶出栈

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