operator return value issue

Question

I am having an issue with a return value with a += operator.

the following is the specific code that is related. If more code needs to be shown I will provide it:

    double operator+=(double b, const Account& c)
    {
      return b += c.getBalance();
    }

where it is implemented in the main:

    for(int i = 0; i < NUMBER_OF_ACCOUNTS; i++)
    {
        std::cout << i+1 << "- " << (balance += *AC[i]) << std::endl;
    }
    std::cout << "Total Balance: " << balance << std::endl;

output I am receiving:

1- 10302.98
2- 10302.98
3- 201.00
Total Balance: 0.00

output I am trying to get:

1- 10302.98
2- 20605.96
3- 20806.96
Total Balance: 20806.96

Don't use * characters to highlight code. That makes the code more confusing. Also, please post a minimal reproducible example — PaulMcKenzie
– PaulMcKenzie, Commented Jun 26, 2016 at 20:24
Why are you returning b += c.getBalance();? Value of b will only change in operator+= function scope (as b is passed by value, not by reference). I think that what you really want to do is return b + c.getBalance(); or perhaps pass b as reference double operator+=(double& b, const Account& c); and then increment it before returning b += c.getBalance(); return b. — Jezor
– Jezor, Commented Jun 26, 2016 at 20:27

izaak_pyzaak · Accepted Answer · 2016-06-26 20:34:11Z

1

You need to pass in b by reference:

double operator+=(double &b, const Account& c)
{
  return b += c.getBalance();
}

instead of

double operator+=(double b, const Account& c)
{
  return b += c.getBalance();
}

Otherwise, think about what happens, the value of balance(0) is copied in with every call, rather than you actually summing to the memory location aliased by balance.

edited Jun 26, 2016 at 20:34

answered Jun 26, 2016 at 20:28

izaak_pyzaak

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2 Comments

izaak_pyzaak Over a year ago

Please repost with a minimum example rather than all your code :) It's now harder to read what your asking than *** highlight ***. ;)

a-one Over a year ago

ok just reposted, I was told to provide a working version earlier, I am still trying to get used to the format that is supposed to used to be posted. Thanks for the answer again it is much appreciated!

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