Questions related to C language data structure stack

1. Implementation principle of stack

#include <stdio.h>

char stack[512];
int top = 0;

void push(char c);
char pop(void);
int is_empty(void);

int main(void)
{
	push('a');
	push('b');
	push('c');

	while(!is_empty())
	{
		putchar(pop());
	}
	printf("\n");

	return 0;
}

void push(char c)
{
	stack[top++] = c;
}

char pop(void)
{
	return stack[--top];
}

int is_empty(void)
{
/*
	if(top == 0)
		return 1;
	else
		return 0;
*/
	return top == 0;
}

2. Application of stack-----Reverse Polish notation

#include <stdio.h>
#include <string.h>

int stack[512];
int top = 0;

void push(int c);
int pop(void);
int is_empty(void);

int main(void)
{
	char a[100];
	int n;
	int i;
	int n1, n2;

	printf("Please enter a reverse polish expression:\n");
	gets(a);
	n = strlen(a);
	
	for(i = 0; i < n; i++)
	{
		if((a[i] >= '0') && (a[i] <= '9'))
			push(a[i] - '0');
		else
		{
			n2 = pop();
			n1 = pop();
			switch(a[i])
			{
				case '+':
					push(n1 + n2);
					break;
				case '-':
					push(n1 - n2);
					break;
				case '*':
					push(n1 * n2);
					break;
			}
		}
	}
	printf("result = %d\n", pop());

	return 0;
}

void push(int c)
{
	stack[top++] = c;
}

int pop(void)
{
	return stack[--top];
}

int is_empty(void)
{
/*
	if(top == 0)
		return 1;
	else
		return 0;
*/
	return top == 0;
}

3. Application of stack----converting infix notation to suffix notation

#include <stdio.h>
#include <string.h>

char stack[512];
int top = 0;

void push(char c);
char pop(void);
int is_empty(void);

int main(void)
{
	char str[100];
	int i, len;

	printf("Please enter a calcuate expression:");
	gets(str);
	
	len = strlen(str);

	for(i = 0; i < len; i++)
	{
		if(str[i] == '(')
			continue;
		else if((str[i] >= '0') && (str[i] <= '9'))
			printf("%c", str[i]);
		else if((str[i] == '+') || (str[i] == '-') || (str[i] == '*'))
			push(str[i]);
		else if(str[i] == ')')
			printf("%c", pop());
	}
	printf("\n");

	return 0;
}

void push(char c)
{
	stack[top++] = c;
}

char pop(void)
{
	return stack[--top];
}

int is_empty(void)
{
/*
	if(top == 0)
		return 1;
	else
		return 0;
*/
	return top == 0;
}

4. Stack application----bracket matching

#include <stdio.h>
#include <string.h>

int stack[512];
int top = 0;

void push(int c);
int pop(void);
int is_empty(void);

int main(void)
{
	char str[100];
	int i, len;

	printf("Please enter a calculate expression:");
	gets(str);
	len = strlen(str);

	for(i = 0; i < len; i++)
	{
		if(str[i] == '(')
			push(i);
		else if(str[i] == ')')
			printf("%d %d\n", pop(), i);
	}

	return 0;
}

void push(int c)
{
	stack[top++] = c;
}

int pop(void)
{
	return stack[--top];
}

int is_empty(void)
{
/*
	if(top == 0)
		return 1;
	else
		return 0;
*/
	return top == 0;
}

5. Stack application----palindrome determination

#include <stdio.h>
#include <string.h>

char stack[512];
int top = 0;

void push(char c);
char pop(void);
int is_empty(void);
int is_palindrom(char *pt);

int main(void)
{
	char str[100];

	printf("Please enter a string:");
	gets(str);

	if(is_palindrom(str))
		printf("str is a palindrom.\n");
	else
		printf("str is not a palindrom.\n");


	return 0;
}

void push(char c)
{
	stack[top++] = c;
}

char pop(void)
{
	return stack[--top];
}

int is_empty(void)
{
/*
	if(top == 0)
		return 1;
	else
		return 0;
*/
	return top == 0;
}

int is_palindrom(char *pt)
{
	int len, i;

	len = strlen(pt);

	for(i = 0; i < len/2; i++)
		push(pt[i]);

	if(len % 2 == 1)
		i++;

	while(!is_empty())
	{
		if(pop() == pt[i])
			i++;
		else
			return 0;
	}
	return 1;
}