#include<stdio.h> //standard input output functions
#include<conio.h> //console functions
#include<string.h> //string functions
#define MAX 50 //max size defined
int stack[MAX]; //a global stack
char post[MAX]; //a global postfix stack
int top=-1; //initializing top to -1
void pushstack(int tmp); //push function
void evaluate(char c); //calculate function
void main()
{
int i,l;
//clrscr();
printf("Insert a postfix notation :: ");
gets(post); //getting a postfix expression
l=strlen(post); //string length
for(i=0;i<l;i++)
{
if(post[i]>='0' && post[i]<='9')
{
pushstack(i); //if the element is a number push it
}
if(post[i]=='+' || post[i]=='-' || post[i]=='*' ||
post[i]=='/' || post[i]=='^') //if element is an operator
{
evaluate(post[i]); //pass it to the evaluate
}
} //print the result from the top
printf("\n\nResult :: %d",stack[top]);
getch();
}
void pushstack(int tmp) //definiton for push
{
top++; //incrementing top
stack[top]=(int)(post[tmp]-48); //type casting the string to its integer value
}
void evaluate(char c) //evaluate function
{
int a,b,ans; //variables used
a=stack[top]; //a takes the value stored in the top
stack[top]='\0'; //make the stack top NULL as its a string
top--; //decrement top's value
b=stack[top]; //put the value at new top to b
stack[top]='\0'; //make it NULL
top--; //decrement top
switch(c) //check operator been passed to evaluate
{
case '+': //addition
ans=b+a;
break;
case '-': //subtraction
ans=b-a;
break;
case '*': //multiplication
ans=b*a;
break;
case '/': //division
ans=b/a;
break;
case '^': //power
ans=b^a;
break;
default:
ans=0; //else 0
}
top++; //increment top
stack[top]=ans; //store the answer at top
}
