Arithmetic Operators

We can use standard arithmetic operators when working with numbers.

• + (addition)
• - (subtraction)
• * (multiplication)
• / (division)
• ** (exponentiation)
• % (modulo)

All of these operators probably look familiar except for one. The modulo operator (%) returns the remainder of division (we’ll explain this further later). For now, run these one line at a time in the Repl.it shell.

Ruby evaluates certain operations with higher precedence, as per the mathematical order of operations, where parentheticals are executed first, then exponentiation, then multiplication and division, then addition and subtraction. 4 - 2 * 5 returns -6 because Ruby evaluates 2 * 5 before 4 - 2. To give an operation highest precedence, wrap it in parentheses.

If you look back at the shell, you'll notice that the division operator probably behaved differently than you would expect. After dividing 9 by 2, the result was 4 instead of 4.5. When we divide two integers, Ruby does not return a fractional number. It instead rounds down to an integer. Most programming languages work similarly. There is some sense to this behavior. If a donut costs $2, and you have $9, how many donuts can you buy? Assuming that the donut shop won't sell you half a donut, you can buy at most 4 donuts.

If you want a fractional answer, you'll want to use floats. Test the following in the shell. (The comments indicate the return value.)

When one or both operands are floats, the operation returns a float (a fractional number with a decimal point), even when the operands divide evenly. The interpreter does not round down a float.

One last interesting operator is the modulo operator (%). The modulo operator (%) returns the remainder of division. This is often useful when determining whether one number evenly divides another. The modulo operator accepts both integers and floats and follows the same rules as the division operator when determining the data type of its output. Try these examples: