Calculator with Functions

Question

I wanna program a simple calculator. The calculations are in functions. My problem is, the result is always 0. :( What is wrong? Look at my code please:

#include "stdafx.h"
#include <stdlib.h>
#include <stdio.h>

double addition(double a,double c);
double subtraktion(double a, double c);
double multiplikation(double a, double c);
double division(double a, double c);



int main()
{
  double z=0, a, c;
  char b;
  printf("Insert your Numbers to calculate!");
  scanf_s("%lf", &a);
  scanf_s("%c", &b);
  scanf_s("%lf", &c);
  if (b == '+')
  {
    addition(a, c);
  }
  if (b == '-')
  {
    subtraktion(a, c);
  }
  if (b == '*')
  {
    multiplikation(a, c);
  }
  if (b == '/')
  {
    division(a, c);
  }
  printf("Result:  %lf", z);
  system("pause");
}

double addition(double a, double c)
{
  double z;
  z = a + c;
  return(z);
}

double subtraktion(double a, double c)
{
  double z;
  z = a - c;
  return(z);
}

double multiplikation(double a, double c)
{
  double z;
  z = a*c;
  return(z);
}

double division(double a, double c)
{
  double z;
  z = a / c;
  return(z);
}

I program with Visual Studio 2013. I tried to debug the Program but this don´t work. Please forgive me my bad English.

Answer 1

I tried this code and it works properly:

#include <stdlib.h>
#include <stdio.h>

double addition(double a,double c);
double subtraktion(double a, double c);
double multiplikation(double a, double c);
double division(double a, double c);



int main()
{
  double z=0, a, c;
  char b;
  printf("Insert your Numbers to calculate!");
  scanf("%lf", &a);
  scanf("%c", &b);
  scanf("%lf", &c);
  if (b == '+')
  {
    z = addition(a, c);
  }
  if (b == '-')
  {
    z = subtraktion(a, c);
  }
  if (b == '*')
  {
    z = multiplikation(a, c);
  }
  if (b == '/')
  {
    z = division(a, c);
  }
  printf("Result:  %lf\n", z);
}

double addition(double a, double c)
{
  double z;
  z = a + c;
  return(z);
}

double subtraktion(double a, double c)
{
  double z;
  z = a - c;
  return(z);
}

double multiplikation(double a, double c)
{
  double z;
  z = a*c;
  return(z);
}

double division(double a, double c)
{
  double z;
  z = a / c;
  return(z);
}

Compile and then in input type: 3+2 [Press enter] and it shows the exact result!

P.S. I deleted the 'custom' header and then used the simple scanf function. I deleted the system("pause") too because I'm not under Visual Studio. (so you may need that)

So what I've done is:
- Deleted your custom header #include "stdafx.h"
- Edited the scanf_s to scanf(...)
- Added z = functions()
- printf(...\n) // not necessary

And it works.

Answer 2

Nowhere are you assigning the results of the operation to z. Instead of:

if (b == '+')
{
    addition(a, c);

 }

You should do

if (b == '+')
{
    z = addition(a, c);

 }

And likewise for all the other cases