How to convert this example of nested ternary if-else to if-else loop

Question

How to convert this example of nested ternary constructor to if-else loop. I am an begginer and is complicated form me.

    int bill = 2000;
    int qty = 10;
    int days = 10;
    int discount = (bill > 1000)? (qty > 11)? 10 : days > 9? 20 : 30 : 5;
    System.out.println(discount);

Start at the inside and go outwards. This is straightforward, though persnickety. — NomadMaker, Mar 31 '21 at 18:35

score 2 · Accepted Answer · edited Mar 31 '21 at 17:35

TL;DR: See last code block for answer to question.

First, an if-else statement is not a "loop".
for, while, and do-while are loops.
if is a conditional statement.

The operator precedence of the ? : ternary conditional operator is so low you rarely need to use parentheses for the 3 parts, unless you have embedded assignment operators. E.g. (bill > 1000) ? 30 : 5 is unnecessary, bill > 1000 ? 30 : 5 means the same thing.

Also, for readability, always use spaces around operators.
A? B : C is wrong. It should be A ? B : C.

Now, since the ternary operator is right-associative, you don't need parenthesis when nesting, i.e.
A ? B ? C : D : E means A ? (B ? C : D) : E
A ? B : C ? D : E means A ? B : (C ? D : E)
The nested ? : operator stays intact.

There is no need for the parenthesis, however keep this in mind. A ? B : (C ? D : (E ? F : G)) is like an if-elseif-elseif-else statement, so the following are equivalent:

// single line
x = A ? B : C ? D : E ? F : G;

// wrapped for readability, to show structure
x = A ? B :
    C ? D :
    E ? F : G;

// using if statement
if (A) {
    x = B
} else if (C) {
    x = D
} else if (E) {
    x = F
} else {
    x = G
}

No parenthesis are needed to clarify the ternary operator if adequate wrapping/indentation is used.

In contrast, A ? (B ? C : D) : E is a nested if statement, so should have parenthesis to clarify that:

// single line
x = A ? B ? C : D : E;

// wrapped for readability, to show structure
x = A ? (B ? C
           : D)
      : E;

// using if statement
if (A) {
    if (B) {
        x = C
    } else {
        x = D
    }
} else
    x = E
}

Ok, end of long story. Let's look at the question code:

// from question
int discount = (bill > 1000)? (qty > 11)? 10 : days > 9? 20 : 30 : 5;

// normalized to have parenthesis only around nested operators
int discount = bill > 1000 ? (qty > 11 ? 10 : (days > 9 ? 20 : 30)) : 5;

// refactored for better structure (using only tail-nesting)
int discount = bill <= 1000 ? 5 : (qty > 11 ? 10 : (days > 9 ? 20 : 30));

// wrapped for readability
int discount = bill <= 1000 ? 5 :
               qty > 11 ? 10 :
               days > 9 ? 20 : 30;

// using if statement
int discount;
if (bill <= 1000) {
    discount = 5;
} else if (qty > 11) {
    discount = 10;
} else if (days > 9) {
    discount = 20;
} else {
    discount = 30;
}

How to convert this example of nested ternary if-else to if-else loop

1 Answers1