% --- start of displayed preamble in the book --- input graph % --- end of displayed preamble in the book --- defaultfont:="ptmr8r"; warningcheck:=0; beginfig(1) draw begingraph(2.5in,1.5in); numeric p[]; path r; for j := 0 upto 100: p[j]:=0; endfor gdata ("ages.dat",y, age:=(scantokens y1); p[age]:=p[age] + 1;); r:=(0,0) for j := 1 upto 100: --(j,p[j]) endfor; gdraw r; frame.llft; endgraph; endfig; end;