Practical-Ds & Algo-2 Parenthesis expression check using stacks.c

/*
    Practical no 2 --parenthisis check 

*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

//variable declarations
int top = -1;
char stack[100];
 
// function definitions or prototyping
void push(char);
void pop();
void find_top();
 

 
    // to push elements in stack
    void push(char a){
    	stack[top] = a;
    	top++;
    }
     
    // to pop elements from stack
    void pop(){
    	if (top == -1){
    		printf("This Expression is not Valid\n");
    		exit(0);
    	}	
    	else{		
    		top--;
    	}
    }
    
    // to find top element of stack
    void find_top(){
    	if (top == -1)
    		printf("\nThis Expression is Valid\n");
    	else
    		printf("\nThis Expression is not Valid\n");
    }

//main function 
int main()
{
	int i;
	char a[100];
	printf("Please Enter the Expression\n");
	scanf("%s", &a);
	for (i = 0; a[i] != '\0';i++){
		if (a[i] == '('||a[i] == '['||a[i] == '{'){
			push(a[i]);
		}
		else if (a[i] == ')'|a[i] == ']'|a[i] == '}'){
			pop();
		}
	}
	find_top();
	return 0;
}