2d seq and some array examples for nim

seqsandarrays.nim

# see here also for seq
# https://nimbyexample.com/sequences.html

# pretty print a seq
# or better than just echo it
proc pp(a: seq[ seq[int] ] ) =
  for i in a:
    echo(i)

proc part1() =
  # make the row dim first
  var a = newSeq[ seq[int] ](5)
  # shows the 5 rows allocated and usable
  echo("first version of a only row has been allocated")
  echo(a)
  # assign a new seq to the first row
  a[0] = newSeq[int](5)
  # shows like it should
  echo("2nd version of a first row has a seq[int] assigned and usable")
  echo(a)

  echo("setting a[0][1] to 200")
  a[0][1] = 200

  # pretty print an array
  echo("pretty print the array")
  pp(a)

  # allocate all of the rows
  # leaked some memory on the first row
  for i in 0 ..< 5:
    a[i] = newSeq[int](5)

  echo("pretty print all rows assigned leaked a row!")
  pp(a)

proc part2() =
  # declare an empty seq
  var a : seq[ seq[int ]]
  echo(a)
  # add a single line
  a.add( newSeq[int](5) )
  pp(a)
  # add 4 more lines
  for i in 0 ..< 4:
    a.add( newSeq[int](5) )
  pp(a)
  # seq is variable len so add a long seq on the end
  a.add( newSeq[int](7))
  pp(a)

proc part3() =
  # if you know the size
  # then use an array
  var a : array[ 5, array[5,int] ]
  for i in a:
    echo(i)

part3()