Negative digit...

[EdalatF]

hello everyone i write a program that seperate digits of the logged number but when the number is negative it's not work...
old code:
int _tmain(int argc, _TCHAR* argv[])
{
int x,y,z;
cout << "Please enter a number" << endl;
cin >> x;
y = x % 10;
cout<< y << endl;
z = x / 10;
cout<< z << endl;
getch();
return 0;
}
i solve it by this code:
int _tmain(int argc, _TCHAR* argv[])
{
int x,y,z;
cout << "Please enter a number" << endl;
cin >> x;
y = -x % 10;
cout<< y << endl;
z = x / 10;
cout<< z << endl;
getch();
return 0;
}
i want to understand when user enter a negative number
why the compiler output result is two negative digit in the old code?

[Cubbi]

why the compiler output result is two negative digit in the old code

Why do you expect a different outcome? y % 10 does not mean "the rightmost digit of y", it means "the remainder of the division of y by 10, rounded towards zero¹". It's a mathematical operation, not a string-of-digits operation. -123 / 10 gives -12, -123 % 10 gives -3, so that you can multiply -12 by 10, add the remainder (-3) and get your original number (-123) back.

¹technically, this was implementation-defined behavior until c99/c++11

[MiiNiPaa]

Actually mathematics usually defines remainder as non-negative number (another version exists but some formulas stop working for negative numbers in that case) Usually (-7 / 5) is -2 with remainder 3.
But in computer science these two operations (division and modulus) can behave either way/ You should lear, how is it working on your language/platform.

non-negative remainder (x%y): (x % y) + y) % y)

[Cubbi]

Even Matlab defines remainder as negative in this case. Although, yes, for each programming language, it's important to look up how these operations are defined, to see if a function that obtains the rightmost digit of an integer can be constructed from them.

[MiiNiPaa]

Wolfram Mathematica thinks it is positive :)
As I say there is two systems. Maybe default system is different depending on country, like metric and imperial systems of measurement.