C Calculator with a lot of functions in functions in functions - c

Question

I had programmed first an easy calculator. Now I would like to outsource the individual program components in Functions. The Problem is the switch-part.The program always gives me the default message:Bad operator. Please take a look and give me some tipps.Is something wrong with the pointers and double-pointers?
Here is my code:
#include "stdafx.h"
#include <stdio.h>
#include <stdlib.h>
void newcalc(char*,double*,char*,double*);
double switchfunk(double**, char**, double**);
double readcalc(double**,char**,double**);
double addition(double,double);
double subtraction(double,double);
double multiplication(double,double);
double division(double,double);
int main()
{
double a=0, b=0;
char op='R', restart = 'Y';
newcalc(&restart,&a,&op,&b);
fflush(stdin);
getchar();
return 0;
}
double switchfunk(double** x, char** opp, double** y)
{
printf("\n ---CALCULATOR--- \n\n\n");
switch (**opp)
{
case '+':printf("%lf + %lf = %lf\n", **x, **y, addition(**x, **y)); break;
case '-':printf("%lf - %lf = %lf\n", **x, **y, subtraction(**x, **y)); break;
case '*':printf("%lf * %lf = %lf\n", **x, **y, multiplication(**x, **y)); break;
case '/':printf("%lf / %lf = %lf\n", **x, **y, division(**x, **y)); break;
default:printf("bad operator!");
}
return 0;
}
void newcalc(char* restart,double* x, char* opp, double* y)
{
while (restart != (char*)'N')
{
readcalc(&x, &opp, &y);
switchfunk(&x, &opp, &y);
printf("New Calc? (Y,N) \n");
fflush(stdin);
scanf("%c", &restart);
if (restart != (char*)'Y'&&restart != (char*)'N')
{
printf("Bad input!");
}
}
}
double readcalc(double** x,char** opp,double** y)
{
printf("\n Type your calculation!(z.B.4+7)\n");
scanf("%lf%c%lf",x,opp,y);
return 0;
}
double addition(double a,double b)
{
double c = 0;
c = a + b;
return c;
}
double subtraction(double a, double b)
{
double c = 0;
c = a - b;
return c;
}
double multiplication(double a, double b)
{
double c = 0;
c = a*b;
return c;
}
double division(double a, double b)
{
double c = 0;
c = a / b;
return c;
}
Best regards!

Answer 1

You have so many problems in your code, most of them related to your use of pointers. Here's one problem:
In the newcalc function you have the following condition in a loop:
restart != (char*)'N'
That will not work as you expect, in fact it will always be true and give you an infinite loop.
The reason is that restart is a pointer which points to the location of the local restart variable in the main function. It will never be the same as (char *) 'N' (which is a pointer pointing to address 78).
How to solve this specific problem? To start with, don't have it as an argument, declare it as a local (non-pointer!) variable:
char restart = 'y';
Then use it normally in the loop condition
while (restart == 'y' || restart == 'Y') { ... }
And to hint to more pointer problems, remember that scanf want a pointer to the variable where to store the value?
But in e.g. the readcalc function the variables x, opp and y are pointers to pointers to where the data should be stored, and yet you pass these pointers-to-pointer to scanf:
scanf("%lf%c%lf",x,opp,y);
Here, you should use pointers as argument to readcalc function, but not pointers-to-pointers.
In other words, it should be declared as
double readcalc(double*,char*,double*);
You most likely have many other problems with your (unnecessary) use of pointers and pointers-to-pointers, but these were the ones that really stood out.

Answer 2

I think you are misusing pointers and using addresses rather than the values themselves. Also, you are using pointers to pointers while you are not in need to do so. Take a look at the following code.
#include <stdio.h>
#include <stdlib.h>
void newcalc (char*,double*,char*,double*);
double switchfunk(double*, char*, double*);
double readcalc(double*,char*,double*);
double addition(double,double);
double subtraction(double,double);
double multiplication(double,double);
double division(double,double);
int main()
{
double a=0, b=0;
char op='R', restart = 'Y';
newcalc(&restart,&a,&op,&b);
fflush(stdin);
getchar();
return 0;
}
double switchfunk (double* x, char* opp, double* y)
{
printf("\n ---CALCULATOR--- \n\n\n");
switch ( *opp )
{
case '+':
printf("%lf + %lf = %lf\n", *x, *y, addition(*x, *y));
break;
case '-':
printf("%lf - %lf = %lf\n", *x, *y, subtraction(*x, *y));
break;
case '*':
printf("%lf * %lf = %lf\n", *x, *y, multiplication(*x, *y));
break;
case '/':
printf("%lf / %lf = %lf\n", *x, *y, division(*x, *y));
break;
default:printf("bad operator!");
}
return 0;
}
void newcalc(char* restart,double* x, char* opp, double* y)
{
while ( *restart == 'Y' || *restart == 'y')
{
readcalc(x, opp, y);
switchfunk(x, opp, y);
printf("New Calc? (Y,N) \n");
fflush(stdin);
scanf("%c", restart);
// if (restart != (char*)'Y'&&restart != (char*)'N')
// {
// printf("Bad input!");
// }
}
}
double readcalc(double* x,char* opp,double* y)
{
printf("\n Type your calculation!(z.B.4+7)\n");
scanf("%lf%c%lf",x,opp,y);
return 0;
}
double addition(double a,double b)
{
return a + b;
}
double subtraction(double a, double b)
{
return a - b;
}
double multiplication(double a, double b)
{
return a*b;
}
double division(double a, double b)
{
return a / b;
}