/******************************************************************************
* ERROR5:  "Input strings too long. Applies to numbers and operators."
* ERROR4:  "Operation not possible."
* ERROR3:  "Division by zero."
* ERROR2:  "Unknown operation."
* ERROR1:  "Number contains alphabetic characters."
*
******************************************************************************/
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>
#include <string.h>
#include <math.h>
#include <ctype.h>
 
#define MAX 11
 
 
 
void main()
{
    float Divide1,Divide2 = 0.0;
    void function(char,float,float);
 
    int Num1;
    int Num2,y,v,k=0,x;
    char isdigit(char);
    char Str2[MAX];
    char Str1[MAX];
    char Operator[1];
//do-while loop until Exit is Typed
    do
    {
    printf("\nPlease enter the required calculation\n");
//Get first string
    scanf("%s", Str1);
//Exit program if 'Exit' typed
    if (strcmp(Str1,"Exit") == 0)
         break;
//Get second string
    scanf("%s", Str2);
    if (strcmp(Str2,"Exit") == 0)
         break;
// if numbers entered are above MAX display error
    if (strlen(Str1) > MAX -1)
        printf("ERROR5");
 
    else if (strlen(Str2) > MAX -1)
        printf("ERROR5");
 
        Divide1= atof(Str1);
    Divide2= atof(Str2);
 
        //Calculate Squareroot if string2 is an 'S'
    if  ((*Str2) == 'S')
        printf("=%f\n",sqrt(Divide1) );
//Calculate Reciprocal if string2 is an 'R'
    else if ((*Str2) == 'R')
        printf("=%f\n",1/Divide1 );
 
// Check if strings are alphabetacal
   if ((*Str2 != 'S') & (*Str2 != 'R'))
    {
        y = strlen(Str1);
        for(x = 0; x < y; x++)
        {
            if ((!isdigit(Str1[x])) & (Str1[0] != '-'))
            {
 
                 k = 1;
            }
            else if ((Str1[0] == '-') & (!isdigit(Str1[x+1])))
            {
                k = 1;
            }
        }
        y = strlen(Str2);
        for(x = 0; x < y; x++)
        {
            if ((!isdigit(Str2[x])) & (Str2[0] != '-'))
            {
                k = 1;
            }
             else if ((Str2[0] == '-') & (!isdigit(Str2[x+1])))
            {
                k = 1;
            }
        }
    if (k == 1)
    {
        printf("ERROR1");
    }
    else
    {
        scanf(" %s", &Operator);
        if (strlen(Operator) > 1)
        {
        printf("ERROR2");
        }
 
        Num1= atoi(Str1);
        Num2= atoi(Str2);
//Switch statement to calculate Addition,Subtraction,Multiplication and Division
        switch(Operator)
        {
            case '+':
            printf("= %d", Num1+Num2);
            break;
            case '-':
            printf("= %d \n", Num1-Num2);
            break;
            case '*':
            printf("=%d ", Num1*Num2);
            break;
            case '/':
            function(*Str2,Divide1,Divide2);
            break;
            default:
               printf("ERROR2");
 
        }
    }
    }
    k = 0;
   fflush(stdin);
 
   }
   while(strcmp(Str1, "Exit") != 0);
   getch();
   }
 
 
    //function to display error if divide by '0' else division performed
void function(char Str2, float Divide1, float Divide2)
    {
        if(Str2 == '0')
            printf("ERROR3");
        else
            printf("=%f",Divide1/Divide2);
 
    }

if ((!isdigit(Str1[x])) & (Str1[0] != '-'))

if (! (isdigit(Str1[x]) || (x == 0 && (Str1[0] == '-')))
  k = 1;

scanf(" %s", &Operator);