string s[];
message "input number a: ";
s1 := readstring;
message "input number b: ";
s2 := readstring;
a := scantokens s1;
b := scantokens s2;

def outp(expr op) =
  message "a " & op & " b = " & decimal(a scantokens(op) b) enddef;

outp("+");
outp("-");
outp("*");
outp("div");
outp("mod");

end