I wrote this program in c to check whether the parenthesis is balanced or not using the concept of stack.

#include<stdio.h>
#include<string.h>
#define MAX 100

int top = -1;
int arr[MAX];


void push(int x)
{
    if (top == (MAX - 1))
    {
        printf("error:stack overflow n");
        return;
    }
    top  ;
    arr[top] = x;
}
void pop()
{
    top--;
}
int empty()
{
    
    if (top == -1)
    {
        printf("The stack is empty \n ");
        return 1;
    }
    else{
        return 0;
    }
}

int main()
{
    char str[30];int len;int i;int temp;
    printf("Enter he expression \n ");
    scanf("%d",str);
    len=strlen(str);

    for(i=0;i<len;i  )
    {

        if (str[i] == '(' || str[i] == '{' || str[i] == '[')
        {
            push(str[i]);
        }

        if (str[i] == ')' || str[i] == '}' || str[i] == ']')
        {
            temp=empty();
            if((empty())==1)
            {
                printf("Unbalanced\n ");
                return;
            }
            else if(str[i]==arr[top])
            {
                pop();
            }
        }
    }

   if((empty())==1)
   {
    printf("Balanced\n");
    
   }
   else {
    printf("unbalanced\n");
   }
    
    
    return 0;
}

however whatever the input i give the result i am getting is

Enter he expression
 {{{]])
empty happend
Balanced

i have isolated the problem where my push and pop function are not being called,and the stack is empty regardless of the input. any idea how to fix the code?

CodePudding user response：

There are two problems.

• First one is the scan should be %s not %d.
• second one you pop if(str[i] == arr[Top]) which is always false, so the stack will remain full.

The code below should work fine.

#include <stdio.h>
#include <string.h>
#define MAX 100

int top = -1;
int arr[MAX];

void push(int x)
{
    if (top == (MAX - 1))
    {
        printf("error:stack overflow n");
        return;
    }
    top  ;
    arr[top] = x;
}
void pop()
{
    top--;
}
int empty()
{
    if (top == -1)
    {
        printf("The stack is empty \n ");
        return 1;
    }
    return 0;   
}

int main()
{
    char str[30];
    int len;
    int i;
    int temp;
    printf("Enter he expression \n ");
    scanf("%s", str);
    len = strlen(str);
    for (i = 0; i < len; i  )
    {
        if (str[i] == '(' || str[i] == '{' || str[i] == '[')
        {
            push(str[i]);
            continue;
        }
        if (str[i] == ')' || str[i] == '}' || str[i] == ']')
        {
            if (empty())
            {
                printf("Unbalanceddd\n ");
                return;
            }
            pop();
        }
    }

    if (empty())
    {
        printf("Balanced\n");
    }
    else
    {
        printf("unbalanced\n");
    }
    return 0;
}