postfix evaluation and checking the balance of the parenthesis

here r the codes for 2 famous problems of programming lab (for 1st yr btech students although i did it in my mtech).The language used here is c++.


1. POSTFIX EVALUATION (I got this problem in the entrance exam of IIIT-A)

#include <iostream.h>
#include <conio.h>
#include <stdio.h>
#include <ctype.h>


float a[30],top=-1;
void push(int val)
{
 if(top==29)
 cout<<"\nOVERFLOW";
 else
 {
  top++;
  a[top]=val;
 }

}

void pop(char c)
{ float temp;
switch(c)
{

case '+':  temp=a[top-1]+a[top];top--;a[top]=temp;break;
case '-':   temp=a[top-1]-a[top];top--;a[top]=temp;break;
case '*':   temp=a[top-1]*a[top];top--;a[top]=temp;break;
case '/':   temp=a[top-1]/a[top];top--;a[top]=temp;break;

}

}


void main()
{  char *p=NULL; int i,s=0; char opt;
do
{ top=-1;
clrscr();
cout<<"\nENTER THE POSTFIX NOTATION(separate operator and operand by a space) : ";
gets(p);
for(i=0;p[i]!=NULL;i++)
{

if(p[i]==' ')
continue;

else if(isdigit(p[i]))
{    while(isdigit(p[i]))
{
  s=s*10+p[i]-'0';
  i++;
}
push(s);
s=0;
}
else
pop(p[i]);
}
cout<<"\nANS IS : "<<a[0];
cout<<"\n\nDO YOU WANT TO CONTINUE(y/n) : ";
cin>>opt;

}while(opt=='y'||opt=='Y');
getch();
}




2. CHECKING THE BALANCE OF THE PARENTHESIS  (I got this problem as a lab test)


#include<iostream.h>
#include<conio.h>
#include<stdio.h>
 
int top=-1; char a[30];
 void push(char p)
 {
 if(top==29)
 cout<<"overflow";
 else
 {top++;
 a[top]=p;
 }

 }

     pop(char p)
{
     switch(p)
     {

     case ')' : if(a[top]=='('){top--;return 1;}
     case '}' : if(a[top]=='{'){top--;return 1;}
     case ']' : if(a[top]=='['){top--;return 1;}


     }
     return 0;

}

void main()
{  char *p=NULL;int i,valid=1;char opt='y';


do
{top=-1;    clrscr();     valid=1;
cout<<"\n\nENTER THE INFIX EXPRESSION : ";
gets(p);
for(i=0;p[i]!=NULL;i++)
{

if(p[i]=='('||p[i]=='{'||p[i]=='[')
push(p[i]);
else if(p[i]==')'||p[i]=='}'||p[i]==']')
{
int chk=pop(p[i]);
if(chk==0)
{valid=0;break;}

}
else
continue;
}

 if(valid==1 && top==-1)
 cout<<"\nbrackets are balanced" ;
 else
 cout<<"\nbrackets are not balanced";
cout<<"\n\ndo you wan to test more(y/n) : ";
cin>>opt;

}while(opt=='y'||opt=='Y');
 getch();
}


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