Source code in the plain programming language

The low number is 1.

The high number is 100.

To run:
Start up.
Play the guessing game.
Wait for the escape key.
Shut down.

To play the guessing game:
Pick a secret number between the low number and the high number.
Write "I chose a secret number between " then the low number then " and " then the high number then "." then the return byte on the console.
Loop.
Ask the user for a number.
If the number is the secret number, break.
If the number is less than the secret number, write "  Too low." on the console.
If the number is greater than the secret number, write "  Too high." on the console.
Repeat.
Write "  Well guessed!" on the console.

To ask the user for a number:
Write "Your guess? " to the console without advancing.
Read a string from the console.
If the string is not any integer, write "  Guess must be an integer." on the console; repeat.
Convert the string to the number.
If the number is less than the low number, write "  Guess can't be lower than " then the low number then "." on the console; repeat.
If the number is greater than the high number, write "  Guess can't be higher than " then the high number then "." on the console; repeat.