**Today I was stumped by a very simple yet awesome problem by my friend Sandip**

What is the answer of

**: 7 % -2**

and to the surprise ruby irb printed it as :

**-1**

After some research I what I found about this and why here is explanation and links

**From Ruby Programming Language, O,really**

**Division, Modulo, and Negative Numbers**

When one (but not both) of the operands is negative, Ruby performs the integer division and

modulo operations differently than languages like C, C++, and Java do (but the same as the

languages Python and Tcl). Consider the quotient -7/3. The floating-point result is –2.33. The

result of integer division must be an integer, however, so this number must be rounded. Ruby

rounds toward negative infinity and returns –3. C and related languages round toward zero

instead and return –2. (This is just one way to characterize the results; no floating-point division

is actually done, of course.)

An important corollary of Ruby's definition of integer division is that, in Ruby, -a/b equals

a/-b but may not equal -(a/b).

Ruby's definition of the modulo operation also differs from that of C and Java. In Ruby, –7%3 is

2.

In C and Java, the result is -1 instead. The magnitude of the result differs, of course, because

the value of the quotient differs. But the sign of the result differs, too. In Ruby, the sign of the

result is always the same as the sign of the second operand. In C and Java, the sign of the result is

always the same as the sign of the first operand. (Ruby also provides a remainder method that

behaves, in sign and magnitude, like the C modulo operator.)

More Links I suggest to must see for more better understanding

http://stackoverflow.com/questions/7395205/modulus-operand-in-ruby-compared-to-php

http://en.wikipedia.org/wiki/Modulus_operator#Remainder_calculation_for_the_modulo_operation

http://www.ruby-doc.org/core-1.9.3/Numeric.html#method-i-25

http://www.ruby-doc.org/core-1.9.3/Numeric.html#method-i-divmod

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