Solve_Postfix_Expression.c

#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#include<math.h>
#define MAX 20
float STACK[MAX];
int top=-1;
char postfix[100];
int isEmpty()
{
  if(top==-1)
    return 1;
  else
    return 0;
}
int isFull()
{
  if(top==MAX-1)
    return 1;
  else
    return 0;
}
void PUSH(float ch)
{
  if(isFull())
  {
    printf("\nStack Overflow");
    exit(0);
  }
  else
    STACK[++top]=ch;
}
float POP()
{
  if(isEmpty())
  {
    printf("\nStack Underflow");
    exit(0);
  }
  else
    return(STACK[top--]);
}
void solvePostfix()
{
  int i=0;
  float operand1, operand2;
  for(;postfix[i]!='\0';i++)
  {
    char ch=postfix[i];
    if(ch==' ')
      continue;
    if(isdigit(ch) && !isFull())
    {
      PUSH(ch-'0');
      continue;
    }
    else
    {
      if(!isEmpty())
      {
        operand2=POP();
        if(isEmpty())
        {
          printf("\nInsuffienct Operands entered.");
          exit(0);
        }
        operand1=POP();
        switch(ch)
        {
          case '+':
            PUSH(operand1+operand2);
          break;
          case '-':
            PUSH(operand1-operand2);
          break;
          case '*':
            PUSH(operand1*operand2);
          break;
          case '/':
            PUSH(operand1/operand2);
          break;
          case '^':
            PUSH(pow(operand1,operand2));
          break;
          case '%':
            PUSH(remainder(operand1,operand2));
          break;
          default:
          {
            printf("\nUnkown operator recieved");
            exit(0);
          }
        }
      }
      else
      {
        printf("\nStack Underflow");
        exit(0);
      }
    }
  }
  if(!isEmpty())
    printf("\nThe result after solving the entered postfix expression is: %.2f", POP());
}
int main()
{
  printf("\nEnter a postfix expression to solve: ");
  gets(postfix);
  solvePostfix();
}