c program for evaluation of prefix

#include<stdio.h>
#include<conio.h>
void main()
{
int s[30],i,a,b,top=-1;
char p[30];
printf("\n enter your expretion:");
gets(p);
strcat(strrev(p),"(");
printf("%s",p);
for(i=0;p[i]!='(';i++)
{
if(p[i]=='+'||p[i]=='-'||p[i]=='*'||p[i]=='/'||p[i]=='^')
{
a=s[top];
top--;
b=s[top];
printf("\n%d\t%d",a,b);
switch(p[i])
{
case '+':
s[top]=a+b;
printf("\t%d",s[top]);
break;

case '-':
s[top]=a-b;
printf("\t%d",s[top]);
break;

case '*':
s[top]=a*b;
printf("\t%d",s[top]);
break;

case '/':
s[top]=a/b;
printf("\t%d",s[top]);
break;

case '^':
s[top]=a^b;
printf("\t%d",s[top]);
break;
}
}
else
{
top++;
s[top]=p[i]-48;
}
}
printf("%d",s[top]);
getch();
}