Shoelace formula for polygonal area: Difference between revisions

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=={{header|Action!}}==

{{libheader|Action! Tool Kit}}

{{libheader|Action! Real Math}}

<lang Action!>INCLUDE "H6:REALMATH.ACT"

PROC Area(INT ARRAY xs,ys BYTE count REAL POINTER res)

BYTE i,next

REAL x1,y1,x2,y2,tmp1,tmp2

IntToReal(0,res)

IntToReal(xs(0),x1) IntToReal(ys(0),y1)

FOR i=0 TO count-1

DO

next=i+1

IF next=count THEN

next=0

FI

IntToReal(xs(next),x2) IntToReal(ys(next),y2)

RealMult(x1,y2,tmp1)

RealAdd(res,tmp1,tmp2)

RealMult(x2,y1,tmp1)

RealSub(tmp2,tmp1,res)

RealAssign(x2,x1) RealAssign(y2,y1)

OD

RealAbs(res,tmp1)

IntToReal(2,tmp2)

RealDiv(tmp1,tmp2,res)

RETURN

PROC PrintPolygon(INT ARRAY xs,ys BYTE count)

BYTE i

FOR i=0 TO count-1

DO

PrintF("(%I,%I)",xs(i),ys(i))

IF i<count-1 THEN

Print(", ")

ELSE

PutE()

FI

OD

RETURN

PROC Test(INT ARRAY xs,ys BYTE count)

REAL res

Area(xs,ys,count,res)

Print("Polygon: ")

PrintPolygon(xs,ys,count)

Print("Area: ")

PrintRE(res) PutE()

RETURN

PROC Main()

INT ARRAY

xs(5)=[3 5 12 9 5],

ys(5)=[4 11 8 5 6]

Put(125) PutE() ;clear screen

Test(xs,ys,5)

RETURN</lang>

{{out}}

[https://gitlab.com/amarok8bit/action-rosetta-code/-/raw/master/images/Shoelace_formula_for_polygonal_area.png Screenshot from Atari 8-bit computer]

<pre>

Polygon: (3,4), (5,11), (12,8), (9,5), (5,6)

Area: 30