C++ Program to Check for Balanced Parentheses using Stack

This C++ program, using a stack data strucure, computes whether the given parantheses expression is valid or not by checking whether each parentheses is closed and nested in the input expression.

Here is the source code of the C++ program to display if it is a balanced expreesion or an invalid string. This C++ program is successfully compiled and run on DevCpp, a C++ compiler. The program output is given below.

```
/*
```

 * C++ Program to Check for balanced paranthesis by using Stacks

```
 */
```
```
#include <iostream>
```
```
#include <conio.h>
```
```
using namespace std;
```
```
struct node
```
```
{
```
```
    char data;
```
```
    node *next;
```

}*p = NULL, *top = NULL, *save = NULL,*ptr;

```
void push(char x)
```
```
{
```
```
    p = new node;
```
```
    p->data = x;
```
```
    p->next = NULL;
```
```
    if (top == NULL)
```
```
    {
```
```
        top = p;
```
```
    }
```
```
    else
```
```
    {
```
```
        save = top;
```
```
        top = p;
```
```
        p->next = save;
```
```
    }
```
```
}
```
```
char pop()
```
```
{
```
```
    if (top == NULL)
```
```
    {
```
```
        cout<<"underflow!!";
```
```
    }
```
```
    else
```
```
    {
```
```
        ptr = top;
```
```
        top = top->next;
```
```
        return(ptr->data);
```
```
        delete ptr;
```
```
    }
```
```
}  
```
```
int main()
```
```
{
```
```
    int i;
```
```
    char c[30], a, y, z;
```
```
    cout<<"enter the expression:\n";
```
```
    cin>>c;
```
```
    for (i = 0; i < strlen(c); i++)
```
```
    {
```

	if ((c[i] == '(') || (c[i] == '{') || (c[i] == '['))

```
	{
```
```
            push(c[i]);
```
```
	}
```
```
	else 
```
```
	{
```
```
	    switch(c[i])
```
```
	    {
```
```
		case ')':
```
```
                         a = pop(); 
```

		         if ((a == '{') || (a == '['))

```
			 {
```
```
			     cout<<"invalid expr!!";
```
```
                             getch();
```
```
			 }   
```
```
			 break;
```
```
		case '}':
```
```
                         y = pop();
```
```
			 if ((y == '[') || (y == '('))
```
```
			 {
```
```
			     cout<<"invalid expr!!";
```
```
                             getch();
```
```
			 }   
```
```
			 break;
```
```
		case ']':
```
```
                         z = pop();
```
```
			 if ((z == '{') || (z == '('))
```
```
			 {
```
```
			     cout<<"invalid expr!!";
```
```
                             getch();
```
```
			 }   
```
```
			 break;
```
```
	    }
```
```
	}
```
```
    }
```
```
    if (top == NULL)
```
```
    {
```
```
	cout<<"balanced expr!!";
```
```
    }
```
```
    else
```
```
    {
```
```
	cout<<"string is not valid.!!";
```
```
    }
```
```
    getch();
```
```
}
```

Output
enter the expression:
[{{{}}}{{()[[]]}}]
balanced expr!!

Sanfoundry Global Education & Learning Series – 1000 C++ Programs.

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