Read two numbers and print their sum
Two prompts that wait for you to type, the numbers coming back in d1, and their sum printed on a line of its own.
The program asks for two numbers, waits while you type them, and prints their sum. Press Run and the
console stops at the first prompt: type a number into the box under it, press Enter, and the run
carries on inside that one trap #15.
Print a string only talked. This one listens, which means the program stops in the middle of an instruction until somebody answers it, and what comes back is a number in a register rather than text you have to make sense of.
You need to know: the "Print a string" Example and the "trap #15 and its tasks" lecture. What is
new here is a task that answers, task 18 leaves the number that was typed in d1.l, so the register
the program reads next is the one the environment wrote.
Task 18 is two tasks in one request: it prints the string at a1 the way task 14 does and then reads
a line and parses it as a decimal number, the way task 4 does. The answer is in d1, which is also
the register task 17 prints from, so the first thing the program does after each read is get the
number out of d1 before the next task overwrites it.
The 10 at the front of second and answer is a newline written as its ASCII code, which is how
you put one inside a string that a task prints. dc.b 10, 'Second number: ', 0 is one string of
seventeen bytes and the first of them is the line break.
Type 17 and 25 and the console reads The sum is 42. Task 4 reads a decimal number and nothing
else, and a line that is not one ends the run with Expected a number, got "NaN" under the editor.
A program that wants to survive what people type reads the line with task 2 and looks at it itself.
Try changing add.l d1, d2 to sub.l d1, d2. With 17 and 25 the console reads The sum is -8,
because task 17 prints d1 as a signed long: the bits FFFFFFF8 are -8 to it and 4294967288 to
task 15.