c++ Reading both left AND right if statement conditions

Question

how do I get the compiler to check both the left and right side of the statement? if I'm not mistaken, i think in C language, it reads both left and right if you have && or || .... so when I looked this up for C++, it says only checks if the left is true....what I need is to be able to check if both sides are true.

so:

//Transactions has been initialized to 0

1. if deposit OR withdraw are greater than or equal to 1, add 1 to variable transactions.
2. if deposit AND withdraw are BOTH greater than or equal 1, then add 2 to variable transactions.
3. else if BOTH are less than 1, transaction is 0.

    if (deposit >= 1 || withdraw >=1)
        {
            transactions = transactions + 1;
            cout << "Transactions:  " << transactions << endl;
        }

    else if (deposit >= 1 && withdraw >=1)
        {
           transactions = transactions + 2;
           cout << "Transactions:  " << transactions << endl;
        }
    else
        {
            cout <<"Transactions: " << transactions << endl;
        }

this issue I'm having is, it reads the left side only, and so transactions only returns 1.

Thank you for your time!

EDIT

https://ideone.com/S66lXi (account.cpp)

https://ideone.com/NtwW85 (main.cpp)

Answer 1

Put the && conditional first and then the || conditional as the else if.

An explanation, courtesy of zenith (+1 him in the comments if this helps you):

The most restrictive case needs to go first, since if A && B is true, A || B will always be true anyway. And thus if you put && after ||, the || case will catch whenever the && case is true.

Also, another side note: leave the cout outside of all the brackets and you can remove the else. It's getting printed no matter what so no need to type it 3 times.

Answer 2

You're not right about C. The || "logical or" operator terminates as soon as one side is true, and it starts to evaluate left to right.

However, that's irrelevant here. Use De Morgan's law to transform your || to (not) and where possible.

Answer 3

You could rewrite the if statements the following way

if (deposit >= 1 && withdraw >=1)
    {
       transactions = transactions + 2;
       cout << "Transactions:  " << transactions << endl;
    }
else if (deposit >= 1 || withdraw >=1)
    {
        transactions = transactions + 1;
        cout << "Transactions:  " << transactions << endl;
    }

else
    {
        cout <<"Transactions: " << transactions << endl;
    }

The other approach is to use the following expression

int condition = ( deposit >= 1 ) + ( withdraw >=1 )

if ( condition == 2 )
    {
       transactions = transactions + 2;
       cout << "Transactions:  " << transactions << endl;
    }
else if ( condition == 1 )
    {
        transactions = transactions + 1;
        cout << "Transactions:  " << transactions << endl;
    }

else
    {
        cout <<"Transactions: " << transactions << endl;
    }

Or simply

 int condition = ( deposit >= 1 ) + ( withdraw >=1 )

 transactions = transactions + condition;
 cout << "Transactions:  " << transactions << endl;

Or

 int condition = ( deposit >= 1 ) + ( withdraw >=1 )

 transactions += condition;
 cout << "Transactions:  " << transactions << endl;

Answer 4

Since both requirement 1 && 2 can evaluate to true, you should take the nested if/else selection statement out of the code. Unfortunately, vlad’s piece of elegant code above will not accurately fulfill the requirements. Since requirement 1 and 2 can both evaluate to true, transactions should have the ability to equal 3.

The code below accurately fulfills your stated requirements.

if (deposit >=1 || withdraw >=1)
    ++transactions;

if (deposit >=1 && withdraw >=1)
    transactions += 2;

if (deposit < 1 && withdraw < 1)
    transactions = 0;

cout << "transactions: " << transactions;

Answer 5

I know this is old, but I want to give my two cents here and really just give people who read this the easiest solution.

operator || will immediately resolve to true and jump in if the first condition it evaluates is true, who cares which one it is?

operator && will only resolve to true and step in when both conditions are evaluated as being true, who cares which one it reads first?

But to answer, C compilers will evaluate the left expression first and short-circuit with operator ||,operator && and operator ,.

It's more logical in my view, and more readable, to evaluate the Boolean expressions separately:

    if(deposit >= 1) {
        transactions += 1;
    }
    if(withdraw >= 1) {
        transactions += 1;
    }

If you wanted to shorthand this, you could do,

int transactions = ((withdraw >= 1) ? 1 : 0) + ((deposit >= 1) ? 1: 0);

but I find that harder to read and sometimes you'll do 0+0, not sure the (in)significance of that.

Because you want to evaluate two different functional requirements that I assume produce different outcomes, keep them separated. Your third functional requirement is already evaluated before you even think about the first two as you've initialised to zero. Just my opinion.

The int condition = ... route is also okay but you're explicitly reserving memory for literally no reason. Not that it particularly matters these days, but C is all about that lower level headache. Plus, my second example does what an earlier comment did without the extra evaluations.

You've taken the if-else route, which is fine when done properly, but you're trying to evaluate a logic problem when it's true, not when it's false, and else will only happen when your condition fails. Forget about trying to gotcha the compiler and think about the logic you're trying to implement, because 9.9999999 times out of 10 it sure ain't the compiler's problem. In fact, the compiler did its job by evaluating what you delegated to it.