用C语言栈写一个后缀表达式计算

下面是用C语言栈实现后缀表达式计算的示例代码：

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

typedef struct stack {
    int top;
    int capacity;
    int *array;
} Stack;

Stack *createStack(int capacity) {
    Stack *stack = (Stack*) malloc(sizeof(Stack));
    stack->top = -1;
    stack->capacity = capacity;
    stack->array = (int*) malloc(stack->capacity * sizeof(int));
    return stack;
}

int isFull(Stack *stack) {
    return stack->top == stack->capacity - 1;
}

int isEmpty(Stack *stack) {
    return stack->top == -1;
}

void push(Stack *stack, int item) {
    if (isFull(stack)) {
        printf("Stack is full\n");
        return;
    }
    stack->array[++stack->top] = item;
}

int pop(Stack *stack) {
    if (isEmpty(stack)) {
        printf("Stack is empty\n");
        return -1;
    }
    return stack->array[stack->top--];
}

int peek(Stack *stack) {
    if (isEmpty(stack)) {
        printf("Stack is empty\n");
        return -1;
    }
    return stack->array[stack->top];
}

int evaluatePostfix(char *exp) {
    Stack *stack = createStack(100);
    int i, operand1, operand2, result;
    for (i = 0; exp[i] != '\0'; ++i) {
        if (isdigit(exp[i])) {
            push(stack, exp[i] - '0');
        } else {
            operand2 = pop(stack);
            operand1 = pop(stack);
            switch (exp[i]) {
                case '+':
                    result = operand1 + operand2;
                    break;
                case '-':
                    result = operand1 - operand2;
                    break;
                case '*':
                    result = operand1 * operand2;
                    break;
                case '/':
                    result = operand1 / operand2;
                    break;
                default:
                    printf("Invalid operator\n");
                    return -1;
            }
            push(stack, result);
        }
    }
    return pop(stack);
}

int main() {
    char exp[] = "231*+9-";
    int result = evaluatePostfix(exp);
    printf("Result: %d\n", result);
    return 0;
}

这个程序的核心在于`evaluatePostfix`函数，它使用了一个栈来计算后缀表达式。具体流程是遍历后缀表达式，如果遇到数字则将其压入栈中，如果遇到运算符则从栈中弹出两个操作数进行计算，并将结果压回栈中。最终栈中只剩下一个元素，即为后缀表达式的计算结果。