Problem Statement

Build an   identity matrix   of a size known at run-time.

An identity matrix is a square matrix of size n × n, where the diagonal elements are all 1s (ones), and all the other elements are all 0s (zeroes).

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{\displaystyle I_{n}={\begin{bmatrix}1&0&0&\cdots &0\0&1&0&\cdots &0\0&0&1&\cdots &0\\vdots &\vdots &\vdots &\ddots &\vdots \0&0&0&\cdots &1\\end{bmatrix}}}

Let's start with the solution:

PROGRAM IDENTITY

!$DYNAMIC
DIM A[0,0]

BEGIN
  PRINT(CHR$(12);) ! CLS
  INPUT("Matrix size",N%)
  !$DIM A[N%,N%]
  FOR I%=1 TO N% DO
    A[I%,I%]=1
  END FOR
! print matrix
  FOR I%=1 TO N% DO
    FOR J%=1 TO N% DO
      WRITE("###";A[I%,J%];)
    END FOR
    PRINT
  END FOR
END PROGRAM