栈

栈（stack）是限定仅在表尾进行插入或删除操作的线性表。栈实现了一种先进后出（last-in, fast-out, 缩写为LIFO）的策略。形象的比喻：生活中的放盘子，最先放的盘子在最下面，最后放的盘子在上面。

栈的实现

#define STACK_INIT_SIZE    100u#define STACKINCREMENT     10u

定义结构体SElemType

typedef struct {int val;}SElemType;

定义结构体SqStack.

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

• base指向栈底。
• top指向栈顶。
• stacksize指示栈的当前可使用的最大容量。

当base值为NULL，表明栈结构不存在。当base=top，表明栈为空。

构造空栈

void InitStack(SqStack *S){S->base = (SElemType *)malloc(STACK_INIT_SIZE * sizeof(SElemType));if (S->base == NULL){exit(0);}S->top = S->base;S->stacksize = STACK_INIT_SIZE;}

销毁栈

void DestroyStack(SqStack *S){free(S->base); S->base = S->top = NULL; S->stacksize = 0;}

清空栈

void ClearStack(SqStack *S){S->top = S->base;}

空栈检测

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

栈的长度

int StackLength(SqStack *S){return (int)(S->top - S->base);}

获取栈顶

void GetTop(SqStack *S, SElemType *e){if (S->top == S->base){exit(0);}else{*e = *(S->top - 1);}}

入栈

void Push(SqStack *S, SElemType *e){if (S == NULL){exit(0);}if (S->top - S->base >= S->stacksize){S->base = (SElemType *)realloc(S->base, (S->stacksize + STACKINCREMENT) * sizeof(SElemType));if (!S->base){exit(0);}S->top = S->base + S->stacksize;S->stacksize += STACKINCREMENT;}*(S->top++) = *e;}

出栈

SElemType Pop(SqStack *S){if (S->top == S->base){exit(0);}return *(--S->top);}

栈的遍历

void StackTraversal(SqStack *S, void (*fp)(SElemType)){SElemType *tmp = S->base;while (tmp < S->top){(*fp)(*tmp);tmp++;}}

栈的操作的序列是直线式的，即先一味地入栈，然后一味地出栈。为什么这一过程不直接用数组实现？当然数组是定长的缺点不是一个确切的答案。这个问题还可以扩展到队列、链表。