#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <math.h>
#include <stdbool.h>
#define ERROR 0
#define MAX 100
#include<iostream>
#include <string.h>
typedef struct //用两个栈来别分存储运算数和运算符double char
{
int top;
double items[MAX];
} DoubleStack;
typedef struct {
int top;
char items[MAX];
} CharStack;
void pushDouble(DoubleStack *s, double item) {
if (s->top < MAX) {
s->top = s->top + 1;
s->items[s->top] = item;
} else {
printf("栈已满。\n");
}
}
double popDouble(DoubleStack *s) {
if (s->top > 0) {
return s->items[s->top--];
} else {
printf("栈为空。\n");
return ERROR;
}
}
void pushChar(CharStack *s, char item) //入栈
{
if (s->top < MAX - 1) {
s->top = s->top + 1;
s->items[s->top] = item;
} else {
printf("栈已满。\n");
}
}
char popChar(CharStack *s) //出栈
{
if (s->top >= 0) {
return s->items[s->top--];
} else {
printf("栈为空。\n");
return '\0';
}
}
char getTop(CharStack *stack) {
if (stack->top >= 0) {
return stack->items[stack->top];
}
return '\0'; // 返回空字符表示栈为空
}
int isoperator(char symbol) //判断char栈中字符是否为运算符
{
if (symbol == '+' || symbol == '-' || symbol == '*' || symbol == '/')
{
return 1; // 返回1表示是运算符
}
else
{
return 0; // 返回0表示不是运算符
}
}
int precedence(char symbol) //判断运算符的优先级 switch case函数
{
switch (symbol) {
case '+':
case '-':
return 1;
case '*':
case '/':
return 2;
default:
return 0;
}
}
double operate(double a, double b, char op) //给出各运算符的运算操作
{
switch (op) {
case '+': return a + b;
case '-': return a - b;
case '*': return a * b;
case '/':
if (b != 0) {
return a / b;
} else {
printf("错误：除数不能为零。\n");
return ERROR;
}
}
}
int expression(char *expression) {
int length = strlen(expression);
int count_bracket = 0;
int last_was_digit = 0;
int has_operator = 0;
int count_operator = 0;
for (int i = 0; i < length; i++) {
char ch = expression[i];
if (isdigit(ch)) {
last_was_digit = 1;
has_operator = 0;
count_operator--;
} else if (isoperator(ch)) {
has_operator = 1;
count_operator++;
last_was_digit = 0;
} else if (ch == '(') {
count_bracket++;
} else if (ch == ')') {
count_bracket--;
if (count_bracket < 0) {
printf("括号不匹配：右括号多于左括号\n");
return 0;
}
} else {
printf("非法字符：%c\n", ch);
return 0;
}
}
if (count_bracket != 0) {
printf("括号不匹配：左括号多于右括号\n");
return 0;
} else if (!last_was_digit || count_operator > 0) {
printf("算术表达式不合法\n");
return 0;
} else {
printf("括号匹配正确，算术表达式合法\n");
return 1;
}
}
void infixToPostfix(const char *infix, char *postfix) {
CharStack stack; //字符栈
stack.top=-1; //将其置空
int i = 0, j = 0; //i j分别用来遍历infix和postfix
char c;
while (infix[i] != '\0') //只要infxi[i]不为空
{
c = infix[i];
if (isdigit(c)) //如果c为数字
{
postfix[j++] = c; // 直接输出数字到postfix
}
else if (isoperator(c)) //如果c为运算符
{
while (precedence(getTop(&stack)) >= precedence(c)) //判断此运算符的优先级 如果优先级小则把栈顶运算符弹出 进入postfix
{
postfix[j++] = popChar(&stack);
}
pushChar(&stack, c); //如果优先级大则入栈
}
else if (c == '(') { //括号的入栈：遇见左括号直接入字符栈
pushChar(&stack, c);
}
else if (c == ')') //当遇到右括号时
{
while (getTop(&stack) != '(') //在遇见左括号之前一直弹出栈中字符
{
postfix[j++] = popChar(&stack);
}
popChar(&stack); // 最后弹出左括号
}
i++; //i进行循环+1
}
while (stack.top >= 0) //将栈里剩余的字符弹出
{
postfix[j++] = popChar(&stack);
}
postfix[j] = '\0'; // 结尾添加空字符
}
void evaluatePostfix(char* postfix, DoubleStack* stack)
{
char ch;
double a, b, value;
int i = 0;
while (postfix[i] != '\0') {
ch = postfix[i++];
if (isdigit(ch))
{
pushDouble(stack,ch-'0' );
}
else if (isoperator(ch))
{
b = popDouble(stack);
a = popDouble(stack);
value = operate(a, b, ch);
pushDouble(stack, value);
printf("计算: %.2f %c %.2f = %.2f\n", a, ch, b, value);
}
}
}
int main()
{
char infix[MAX], postfix[MAX];
DoubleStack stack;
stack.top = -1;
printf("请输入算术表达式: ");
scanf("%s", infix);
if (expression(infix)) {
infixToPostfix(infix, postfix);
printf("后缀表达式: %s\n", postfix);
evaluatePostfix(postfix, &stack);
if (stack.top == 0) {
printf("表达式的结果是: %.2f\n", popDouble(&stack));
} else {
printf("表达式无效或者栈操作错误。\n");
}
} else {
printf("输入的表达式无效。\n");
}
return 0;
}
出现如图的问题 第一个操作数为0
