Asking questions

INPUT stops the program, waits for someone to type something, and puts what they typed into a variable.

The shape of it

10 INPUT "HOW OLD ARE YOU"; A
20 PRINT "IN DOG YEARS:"; A * 7

RUN
HOW OLD ARE YOU? 9
IN DOG YEARS: 63

OK

BASIC prints your prompt, adds a ? of its own, and waits. Whatever gets typed lands in A when Enter is pressed.

The prompt is optional — INPUT A on its own just prints ? — but a program that asks a bare question mark is a program nobody can use.

Text answers need a $

10 INPUT "WHAT IS YOUR NAME"; N$
20 PRINT "HELLO, "; N$

Ask for N$ and you get text. Ask for A and you get a number, and BASIC will insist on one.

Asking for several things at once

Put more than one variable after INPUT and the person can answer with commas:

10 INPUT A$, B$
20 PRINT A$; "/"; B$

RUN
? ONE,TWO
ONE/TWO

OK

Nice when you're the one typing. Unkind to anyone else. Two separate INPUTs with two clear prompts is almost always the better program.

When the answer is wrong

Two messages come from INPUT, and neither is an error that stops the program:

?REDO FROM START — you asked for a number and got something that isn't one. BASIC throws the whole answer away and asks again:

RUN
? HELLO
?REDO FROM START
? 5

OK

?EXTRA IGNORED — you asked for one thing and got several. BASIC keeps the first and drops the rest:

RUN
? 5,6
?EXTRA IGNORED
 5

OK

Both are BASIC being forgiving. Neither needs handling in your program.

It only works inside a program

Type INPUT A straight at the OK prompt and you get:

?ILLEGAL DIRECT ERROR

INPUT needs a program to come back to, so it refuses to run in immediate mode. The same goes for GET-style reading of single keys — INKEY is the one to reach for when you want a keypress rather than a line.

A worked example

10 PRINT "WHAT IS YOUR NAME";
20 INPUT N$
30 PRINT "HOW OLD ARE YOU";
40 INPUT A
50 PRINT
60 PRINT "HELLO "; N$; ", IN TEN YEARS"
70 PRINT "YOU WILL BE"; A + 10

RUN
WHAT IS YOUR NAME? ADA
HOW OLD ARE YOU? 30

HELLO ADA, IN TEN YEARS
YOU WILL BE 40

OK

The ; on the end of lines 10 and 30 is what keeps the ? on the same line as the question. Take it off and see what happens — that's the fastest way to understand what it does.

Try this

Add a line 45 that refuses to believe anyone is over 150, using IF — which is the next chapter.