#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#include<math.h>
typedef struct node
{
char info;
struct node *lchild,*rchild;
}NODE;
NODE * create_tree(char postfix[])
{
NODE *newnode, *stack[20];
int i=0, top = -1;
char ch;
while((ch=postfix[i++])!='\0')
{
newnode = (NODE*)malloc(sizeof(NODE));
newnode->info = ch;
newnode->lchild = newnode->rchild = NULL;
if(isalnum(ch))
stack[++top]=newnode;
else
{
newnode->rchild = stack[top--];
newnode->lchild = stack[top--];
stack[++top]=newnode;
}
}
return(stack[top--]);
}
float eval(NODE *root)
{
float num;
switch(root->info)
{
case '+' : return (eval(root->lchild) + eval(root->rchild));
case '-' : return (eval(root->lchild) - eval(root->rchild));
case '*' : return (eval(root->lchild) * eval(root->rchild));
case '/' : return (eval(root->lchild) / eval(root->rchild));
case '^' : return (pow(eval(root->lchild), eval(root->rchild)));
default: if(isalpha(root->info))
{
printf("\n%c = ",root->info);
scanf("%f",&num);
return(num);
}
else
return(root->info - '0');
}
}
int main()
{
char postfix[30];
float res;
NODE * root = NULL;
printf("\nEnter a valid Postfix expression\n");
scanf("%s",postfix);
root = create_tree(postfix);
res = eval (root);
printf("\nResult = %f",res);
return 0;
}