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1. Multiply by -1
If you have a number that's positive/negative and want to convert it to negative/positive, then this is one way to do this:

var nr, x, y;
nr = 500;
x = nr * -1; // x is the negative value of nr (-500)
y = x * -1; // y is the negative value of x (500)

if(nr == y) // This is always the same, so what's in it will always be executed.
{
  show_message("This always get's executed!");
}

2. Divide by -1
The same works with diving it by -1:

var nr, x, y;
nr = 500;
x = nr / -1; // x is the negative value of nr (-500)
y = x / -1; // y is the negative value of x (500)

if(nr == y) // This is always the same, so what's in it will always be executed.
{
  show_message("This always get's executed!");
}

3. Zero minus the number
Another way to do it is in this way:

var nr, x, y;
nr = 500;
x = 0 - nr; // x is the negative value of nr (-500)
y = 0 - x; // y is the negative value of x (500)

if(nr == y) // This is always the same, so what's in it will always be executed.
{
  show_message("This always get's executed!");
}

4. Just put a minus in front of the variable
This is the easiest way, and it actually works the same as the third.

var nr, x, y;
nr = 500;
x = -nr; // x is the negative value of nr (-500)
y = -x; // y is the negative value of x (500)

if(nr == y) // This is always the same, so what's in it will always be executed.
{
  show_message("This always get's executed!");
}

5. Minus itself multiplied by two:
And another way:

var nr, x, y;
nr = 500;
x = nr; // Init x to nr
x -= x * 2; // x is the negative value of nr (-500)
y = x; // Init y to x
y -= y * 2; // y is the negative value of x (500)

if(nr == y) // This is always the same, so what's in it will always be executed.
{
  show_message("This always get's executed!");
}

6. Direct multiply by -1
This is a bit different, just like fifth way it can only be applied to the variable itself.

var nr, x, y;
nr = 500;
x = nr; // Init x to nr
x *= -1; // x is the negative value of nr (-500)
y = x; // Init y to x
y *= -1; // y is the negative value of x (500)

if(nr == y) // This is always the same, so what's in it will always be executed.
{
  show_message("This always get's executed!");
}

This way is pretty easy to use.
» fold ways to switch between negative and positive «

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1. Using an if-statement
I think that everyone knows how this is achieved using an if statement:

var nr1, nr2;
nr1 = -200;
nr2 = 300;

if(nr1 < 0) nr1 *= -1;
if(nr2 < 0) nr2 *= -2;

show_message(string(nr1)); // 200
show_message(string(nr2)); // 300

2. Using math

var nr1, nr2;
nr1 = -200;
nr2 = 300;

nr1 = sqrt(sqr(nr1));
nr2 = sqrt(sqr(nr2));

show_message(string(nr1)); // 200
show_message(string(nr2)); // 300

» fold tricks to make numbers always positive «

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I know a lot of programmers who are used to use RGB (Red, Green, Blue) as their only color spectrum.
Though HSV (Hue Saturation Value) offers you ways to make smooth color motions.
How HSV works is pretty simple. The Saturation stand for the amount of color. While the Value means the lightness or brightness.
The Hue however is the actual color. In GM all those values go from 0 to 255. But with the Hue 255 is equal to zero.
As example:

var color1, color2, color3;
color1 = $FF0000; // GM Color Code (HEX)
color2 = make_color_rgb(255, 0, 0); // The RGB Color
color3 = make_color_hsv(0, 255, 255); // The HSV Color

All of those variables are the same, the color red.
Another example:

var color1, color2, color3;
color1 = $00FF00; // GM Color Code (HEX)
color2 = make_color_rgb(0, 255, 0); // The RGB Color
color3 = make_color_hsv(85, 255, 255); // The HSV Color

All those variables represent the color green.
And the color blue is:

var color1, color2, color3;
color1 = $0000FF; // GM Color Code (HEX)
color2 = make_color_rgb(0, 0, 255); // The RGB Color
color3 = make_color_hsv(170, 255, 255); // The HSV Color

Last, the color white:

var color1, color2, color3;
color1 = $FFFFFF; // GM Color Code (HEX)
color2 = make_color_rgb(255, 255, 255); // The RGB Color
color3 = make_color_hsv(0, 0, 255); // The HSV Color, in this case the Saturation is zero, this means that no color will be visible, so the hue doesn't matter. In most cases the Hue will then be referred to as zero.

Something you could apply this to is this:
Create event:

hue = 0

Step event:

hue += 1;

Draw event:

draw_set_color(make_color_hsv(hue, 255, 255));
draw_set_alpha(1);
draw_rectangle(x, y, x + 16, y + 16, false);

When you place an object with those codes in it in a room it'll be a rectangle of 16x16 of which the color goes around the entire color spectrum.
» fold a tip on the color spectrum «

0

Just create a new file with an object, and a room without changing any properties except maybe the width and height (I have them at 800x600).
Then just add these:


I hope you can learn any more from this.
» fold script for the screen «