用C写后缀表达式求值代码

我可以为您提供C语言中后缀表达式求值的代码：

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

#define STACK_INIT_SIZE 20
#define STACKINCREMENT 10

typedef char ElemType;

typedef struct {
    ElemType *base;
    ElemType *top;
    int stacksize;
} SqStack;

void InitStack(SqStack *S) {
    S->base = (ElemType *) malloc(STACK_INIT_SIZE * sizeof(ElemType));
    if (!S->base)
        exit(1);
    S->top = S->base;
    S->stacksize = STACK_INIT_SIZE;
}

void Push(SqStack *S, ElemType e) {
    if (S->top - S->base >= S->stacksize) {
        S->base = (ElemType *) realloc(S->base,
                                       (S->stacksize + STACKINCREMENT) * sizeof(ElemType));
        if (!S->base)
            exit(1);
        S->top = S->base + S->stacksize;
        S->stacksize += STACKINCREMENT;
    }
    *(S->top)++ = e;
}

void Pop(SqStack *S, ElemType *e) {
    if (S->top == S->base)
        return;
    *e = *--S->top;
}

ElemType GetTop(SqStack *S) {
    if (S->top != S->base)
        return *(S->top - 1);
    else
        exit(1);
}

int StackEmpty(SqStack *S) {
    if (S->top == S->base)
        return 1;
    else
        return 0;
}

int EvaluateExpression(char Expression[]) {
    SqStack S;
    InitStack(&S);
    char c, d;
    int i, num, a, b;
    i = num = 0;
    c = Expression[i];
    while (c != '\0') {
        if (isdigit(c)) {
            num = 0;
            while (isdigit(c)) {
                num = num * 10 + c - '0';
                i++;
                c = Expression[i];
            }
            Push(&S, num);
        } else {
            Pop(&S, &a);
            Pop(&S, &b);
            switch (c) {
                case '+':
                    num = b + a;
                    break;
                case '-':
                    num = b - a;
                    break;
                case '*':
                    num = b * a;
                    break;
                case '/':
                    num = b / a;
                    break;
                default:
                    exit(1);
            }
            Push(&S, num);
            i++;
            c = Expression[i];
        }
    }
    Pop(&S, &num);

    return num;
}

int main() {
    char expression[100] = "234*+";
    printf("后缀表达式：%s\n", expression);
    printf("结果为：%d\n", EvaluateExpression(expression));
    return 0;
}

您可以将需要计算的后缀表达式放在 `EvaluateExpresssion` 函数中 `char expression[]` 数组中的引号内。例如，想要计算 "23 4 * 5 +" 的值，可以将 `char expression[100]` 改为 `char expression[100] = "23 4 * 5 +"`，最终结果将会输出至屏幕上。