非递归函数的递归求解

#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#define STACK_INIT_SIZE 20
#define STACKINCREMENT 10

typedef  int ElemType;
typedef struct {
    ElemType *base;
    ElemType *top;
    int stacksize;
} sqStack;
/*初始化栈*/
void initStack(sqStack *s)
{
    /*内存中开辟一段连续空间作为栈空间，首地址赋值给s->base*/
    s->base = (ElemType *)malloc(STACK_INIT_SIZE * sizeof(ElemType));

    if(!s->base) exit(0);                /*分配空间失败*/

    s->top = s->base;                /*最开始，栈顶就是栈底*/
    s->stacksize = STACK_INIT_SIZE;     /*最大容量为STACK_INIT_SIZE */
}
/*入栈操作，将e压入栈中*/
void Push(sqStack *s, ElemType e) {
    if(s->top - s->base >= s->stacksize) {
        /*栈满，追加空间*/
        s->base = (ElemType *)realloc(s->base, (s->stacksize +
                                                STACKINCREMENT) * sizeof(ElemType));

        if(!s->base) exit(0);                                /*存储分配失败*/

        s->top = s->base + s->stacksize;
        s->stacksize = s->stacksize + STACKINCREMENT;        /*设置栈的最大容量*/
    }

    *(s->top) = e;                                             /*放入数据*/
    s->top++;
}
/*出栈操作，用e将栈顶元素返回*/
void Pop(sqStack *s , ElemType *e) {
    if(s->top == s->base) return;

    *e = *--(s->top);
}

int f(int n)
{
    int r = 1, e;
    sqStack stack;
    initStack(&stack);                /*初始化栈*/

    while(n != 0) {
        Push(&stack, n);            /*保存现场n*/
        n = n / 2;
    }

    while(stack.top != stack.base)
    {
        Pop(&stack, &e);
        r = r * e;
    }

    return r;
}

int main()
{
    printf("The result for conversion of recursion to non recursion is\n");
    printf("f(5)=%d \n", f(5));
    return 0;
}