数据结构——栈（C语言实现）

#include <stdio.h>
#include <stdlib.h>
#include<string.h>
#include<malloc.h>
// 栈结构的定义
typedef struct _stack {
    int size;   // 栈存储空间的尺寸
    int* base;   // 栈基址
    int* sp;    // 栈顶
} stack;
 
void init(stack* s, int n) {
    s->base = (int*)malloc(sizeof(int)*n);
    s->size = n;
    s->sp = s->base;
}
 
void push(stack* s, int val) {
    if(s->sp - s->base == s->size) {
        puts("none");
        exit(1);
    }
    *s->sp++ = val;
}
 
int pop(stack* s) {
    if(s->sp == s->base) {
        puts("none");
        exit(2);
    }
    return *--s->sp;
}
int peek(stack*s) {
    if(s->sp == s->base) {
        puts("none");
        exit(2);
    }
 
    return *(s->sp-1);
}
 
int empty(stack* s) {
    return s->sp == s->base;
}
 
void clean(stack* s) {
    if(s->base)
        free(s->base);
}
 
int main(void) {
    stack s;
    int i,n;
    int num;
    char str[30];
    init(&s, 1000);
    while(1) {
 
        scanf("%s",str);
        if(strcmp(str,"push")==0) {
            scanf("%d",&num);
            push(&s, num);
        } else if(strcmp(str,"top")==0) {
            printf("%d\n", peek(&s));
        } else if(strcmp(str,"pop")==0) {
            printf("%d\n", pop(&s));
        } else if(strcmp(str,"clear")==0) {
            empty(&s);
        } else if(strcmp(str,"exit")==0) {
            clean(&s);
 
            break;
        }
    }
    return 0;
}