#include<ctype.h>
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
//Stack type
struct Stack{
int top;
unsigned capacity;
int*array;
};
//Stack Operations
struct Stack*createStack(unsigned capacity)
{
struct Stack*stack
=(struct Stack*)malloc(sizeof(struct Stack));
if(!stack)
return NULL;
stack->top=-1;
stack->capacity=capacity;
stack->array
=(int*)malloc(stack->capacity*sizeof(int));
if(!stack->array)
return NULL;
return stack;
}
int isEmpty(struct Stack*stack)
{
return stack->top==-1;
}
char peek(struct Stack*stack)
{
return stack->array[stack->top];
}
char pop(struct Stack*stack)
{
if (!isEmpty(stack))
return stack->array[stack->top--];
return'$';
}
void push(struct Stack*stack,char op)
{
stack->array[++stack->top]=op;
}
//The main function that returns value
//of a given postfix expression
int evaluatePostfix(char*exp)
{
//Create a stack of capacity equal to expression size
struct Stack*stack=createStack(strlen(exp));
int i;
//See if stack was created successfully
if(!stack)
return-1;
//Scan all characters one by one
for(i=0;exp[i];++i){
//If the scanned character is an operand
//(number here),push it to the stack.
if(isdigit(exp[i]))
push(stack,exp[i]-'0');
//If the scanned character is an operator,
//pop two elements fron stack apply the operator
else{
int val1=pop(stack);
int val2=pop(stack);
switch(exp[i]){
case'+':
push(stack,val2+val1);
break;
case'-':
push(stack,val2-val1);
break;
case'*':
push(stack,val2*val1);
break;
case'/':
push(stack,val2/val1);
break;
}
}
}
return pop(stack);
}
//Driver code
int main()
{
char exp[]="362/-3+";
//Function call
printf("postfix evaluation:%d",evaluatePostfix(exp));
return 0;
}
