Pascal: Validating Real Numbers

program ex8;

var a, b, c, sum: real;
begin
  repeat
    writeln ('Enter a real number');
    readln (a);
    if (a < -100) then writeln ('Number must be -100 or bigger');
    if (a > 100) then writeln ('Number must be 100 or smaller');
  until (a >= -100) and (a <=100);
  repeat
    writeln ('Enter another real number');
    readln (b);
    if (b < -100) then writeln ('Number must be -100 or bigger');
    if (b > 100) then writeln ('Number must be 100 or smaller');
  until (b >= -100) and (b <=100);
repeat
    writeln ('Enter one more real number');
    readln (c);
    if (c < -100) then writeln ('Number must be -100 or bigger');
    if (c > 100) then writeln ('Number must be 100 or smaller');
  until (c >= -100) and (c <=100);
  sum:=a + b + c;
  writeln ('Sum is: ', sum: 8: 2);
  readln;
end.

To ensure numbers entered match criteria (-100-100) we use two techniques again:

• repeat input until number in range
• check size of number and issue error message if wrong

This error trapping does not prevent the user from entering non-numeric data.

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