逆波兰表达式求值的代码c语言实现

下面是逆波兰表达式求值的 C 语言代码示例：

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

#define STACK_SIZE 100

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

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

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

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

void push(Stack *s, int value) {
    if (is_full(s)) {
        fprintf(stderr, "stack is full\n");
        exit(EXIT_FAILURE);
    }
    s->data[++s->top] = value;
}

int pop(Stack *s) {
    if (is_empty(s)) {
        fprintf(stderr, "stack is empty\n");
        exit(EXIT_FAILURE);
    }
    return s->data[s->top--];
}

int main() {
    Stack s;
    init(&s);

    char expression[] = "2 3 + 4 *";  // 2 + 3 * 4 = 14
    char *token = strtok(expression, " ");
    while (token != NULL) {
        if (isdigit(*token)) {
            push(&s, atoi(token));
        } else {
            int b = pop(&s);
            int a = pop(&s);
            switch (*token) {
                case '+': push(&s, a + b); break;
                case '-': push(&s, a - b); break;
                case '*': push(&s, a * b); break;
                case '/': push(&s, a / b); break;
                default:
                    fprintf(stderr, "invalid operator: %c\n", *token);
                    exit(EXIT_FAILURE);
            }
        }
        token = strtok(NULL, " ");
    }

    printf("result: %d\n", pop(&s));
    return 0;
}