Let us review the Lua ternary operator in terms of the if-then-else expression.

Some expressions involve unary operators such as arithmetic negation or logical negation.

Some expressions involve binary operators such as arithmetic addition, subtraction,e etc., or logical conjunction, disjunction, etc.

There is a common ternary operator "?" (question mark) that takes three operands. It is sometimes called a conditional expression (as contrasted with the "if then else") conditional control flow statement. Here is the C code [#1]
#include <stdio.h> int main() { // declarations int x1; int x2; // input scanf("%d",&x1); // process if (x1 < 0) { x2 = - x1; } else { x2 = x1; } // output printf("The absolute value of %d is %d.\n",x1,x2); return 0; }

Here are some examples of input and output for the above program code.

Here is an example input.
-1
For the above example input, here is the expected output.
The absolute value of -1 is 1.
Here is an example input.
1
For the above example input, here is the expected output.
The absolute value of 1 is 1.
Here is an example input.
0
For the above example input, here is the expected output.
The absolute value of 0 is 0.
Here is the C code [#2]
#include <stdio.h> int main() { // declarations int x1; int x2; // input scanf("%d",&x1); // process x2 = (x1 < 0) ? - x1 : x1; // output printf("The absolute value of %d is %d.\n",x1,x2); return 0; }

Here are some examples of input and output for the above program code.

Here is an example input.
-1
For the above example input, here is the expected output.
The absolute value of -1 is 1.
Here is an example input.
1
For the above example input, here is the expected output.
The absolute value of 1 is 1.
Here is an example input.
0
For the above example input, here is the expected output.
The absolute value of 0 is 0.

The ternary expression, or if-then-else expression, has the following general form.

Both then-expression and else-expression are required.

I prefer to usually use parentheses around the condition part of the conditional expression.

By contrast, the if-then-else statement has the following form.

The else-statements (and else-part) can be omitted if not needed. Note: In the above example programs, the use of the ternary operator takes 5 lines (in the if-then-else statement) to one line (using the if-then-else expression).

Python has a ternary operator or if-then-else expression.

Consider the following example program that computes and outputs the absolute value of the elements of the list using an if-then-else statement. Here is the Python code [#1]
list1 = [-1, 0, 1] for x1 in list1: if x1 < 0: x2 = - x1 else: x2 = x1 print("The absolute value of {0:d} is {1:d}.".format(x1,x2))
Here is the output of the Python code.
The absolute value of -1 is 1. The absolute value of 0 is 0. The absolute value of 1 is 1.

Now consider the following example program that does the same thing but uses the ternary operator using an if-then-else expression.

Here is the Python code [#2]
list1 = [-1, 0, 1] for x1 in list1: x2 = -x1 if x1 < 0 else x1 print("The absolute value of {0:d} is {1:d}.".format(x1,x2))
Here is the output of the Python code.
The absolute value of -1 is 1. The absolute value of 0 is 0. The absolute value of 1 is 1.