Question

Write a program to check the mathematical expressions containing the following parentheses for validity:

                (

                [

                {

Hint: {(6 – 2) * 8} is a valid expression. [3 + (6 * 7) } is an invalid expression.

Answer 1

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

int top = -1;
char stack[100];

// function prototypes
void push(char);
void pop();
void find_top();

void main()
{
   int i;
   char a[100];
   printf("enter expression\n");
   scanf("%s", &a);
   for (i = 0; a[i] != '\0';i++)
   {
       if (a[i] == '(')
       {
           push(a[i]);
       }
       else if(a[i]=='{')
{

push(a[i]);
}
else if(a[i]=='[')
{

push(a[i]);
}
       else if (a[i] == ')')
       {
           pop();
       }
       else if(a[i]=='}')
{

pop();
}
else if(a[i]=']')
{

pop();
}
   }
   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("expression is invalid\n");
       exit(0);
   }
   else
   {
       top--;
   }
}

// to find top element of stack
void find_top()
{
   if (top == -1)
       printf("\nexpression is valid\n");
   else
       printf("\nexpression is invalid\n");
}

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out put

enter expression
{3+(2*3))
expression is invalid