c语言计算后缀表达式

以下是C语言计算后缀表达式的代码示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_SIZE 100

typedef struct Stack {
    int top;
    int data[MAX_SIZE];
} Stack;

void init(Stack *s) {
    s->top = -1;
}

int is_empty(Stack *s) {
    return s->top == -1;
}

int is_full(Stack *s) {
    return s->top == MAX_SIZE - 1;
}

void push(Stack *s, int x) {
    if (is_full(s)) {
        printf("Stack is full.\n");
        exit(1);
    }
    s->data[++s->top] = x;
}

int pop(Stack *s) {
    if (is_empty(s)) {
        printf("Stack is empty.\n");
        exit(1);
    }
    return s->data[s->top--];
}

int calculate(int a, int b, char op) {
    switch (op) {
        case '+':
            return a + b;
        case '-':
            return a - b;
        case '*':
            return a * b;
        case '/':
            return a / b;
        default:
            printf("Invalid operator.\n");
            exit(1);
    }
}

int evaluate(char *expr) {
    Stack s;
    init(&s);
    char *token = strtok(expr, " ");
    while (token != NULL) {
        if (isdigit(token[0])) {
            push(&s, atoi(token));
        } else {
            int b = pop(&s);
            int a = pop(&s);
            push(&s, calculate(a, b, token[0]));
        }
        token = strtok(NULL, " ");
    }
    return pop(&s);
}

int main() {
    char expr[MAX_SIZE];
    printf("Enter postfix expression: ");
    fgets(expr, MAX_SIZE, stdin);
    expr[strlen(expr) - 1] = '\0';
    int result = evaluate(expr);
    printf("Result: %d\n", result);
    return 0;
}