C程序设计语言 4-4

 练习4-4 在栈操作中添加几个命令，分别用于在不弹出元素的情况下打印栈顶元素；复制栈顶元素；交换栈顶两个元素的值。另外增加一个命令用于清空栈。

最后添加一个简单测试。

#include 

#define MAXVAL 100

int sp = 0;
double val[MAXVAL];

void push(double f)
{
	if (sp < MAXVAL)
		val[sp++] = f;
	else
		printf("error: stack full, can't push %g\n", f);
	
	return;
}

double pop(void)
{
	if (sp > 0)
		return val[--sp];
	else
	{
		printf("error:stack empty\n");
		return 0.0;
	}
}

void print_no_pop(void)
{
	if (sp > 0)
		printf("%g\n", val[sp-1]);
	else
		printf("error:stack empty\n");
	
	return;
}

void stack_top_cpy(void)
{
	if (sp > 0 || sp < MAXVAL)
		val[sp++] = val[sp-1];
	else if (sp <= 0)
		printf("error:stack empty\n");
	else
		printf("error:stack full\n");
	
	return ;
}

void swap_stack_top(void)
{
	double temp;
	if (sp >= 2)
	{
		temp = val[sp-1];
		val[sp-1] = val[sp-2];
		val[sp-2] = temp;
	}
	else
		printf("not enough number\n");
	
	return;
}

void empty_stack(void)
{
	sp = 0;
	return;
}

int main()
{
	double i;
	for (i = 1.0; i < 20.0; i++)
		push(i);
	printf("affirm:%g\n", pop());
	swap_stack_top();
	printf("swap:%g\n", pop());
	printf("swap:%g\n", pop());
	stack_top_cpy();
	printf("copy:%g\n", pop());
	printf("copy:%g\n", pop());
	printf("print_no_pop:\n");
	print_no_pop();
	empty_stack();
	printf("empty:%g\n", pop());
	
	return 0;
}