strange behavior from numeric keypad

Projects Programming
1

I've written a function that takes in values from a 4X3 numeric keypad and compares them with numbers to decide which compartment to use in a candy vending machine project my son is working on.) It's supposed to return "invalid choice" for anything other than the numbers 1 and 2 from the keypad. It works fine for 1 and 2 and returns invalid for all other numbers except 8,9 or *. If I input any of these numbers, they're interpreted as valid under the strcmp '2' condition. I'm stumped as to why these characters are being equated with '2'. Can anyone enlighten me?

#include <Keypad.h>
const byte ROWS = 4; //four rows
const byte COLS = 3; //four columns

int Candy_choice;
boolean Candy_chosen = false;
int Which_candy;

char Key_pressed;

//define the symbols on the buttons of the keypads
char hexaKeys[ROWS][COLS] = {
{'1','2','3'},
{'4','5','6'},
{'7','8','9'},
{'*','0','#'}
};

byte rowPins[ROWS] = {9, 8, 7, 6}; //connect to the row pinouts of the keypad
byte colPins[COLS] = {5, 4, 3}; //connect to the column pinouts of the keypad
//initialize an instance of class NewKeypad
Keypad My_Keypad = Keypad( makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS);

void Get_choice()
{
Serial.print("Enter choice: ");
while(! Candy_chosen) //if the user hasn't chosen which candy they want
{
Key_pressed = My_Keypad.getKey(); //wait for a key to be input
if (Key_pressed) //a key has been pressed
{
Serial.println(Key_pressed);
if(!strcmp('1', Key_pressed)) //if the key is "1"
{
Which_candy = 1; //set the candy choice to 1
Candy_chosen = true; //set the candy chosen flag to true
Serial.print("Enter password: "); prompts user for password
return; //return to main loop
}
else
if(!strcmp('2', Key_pressed))
{
Which_candy = 2;
Candy_chosen = true;
Serial.print("Enter password: ");
return;
}
else
{
Serial.println("invalid choice");
delay(500);
Serial.print("Enter choice: ");
}
}
}
}

2

Suggest you spend some time with a few tutorials.

https://playground.arduino.cc/Main/KeypadTutorial

.

3

Many, many errors in this code. strcmp() expects zero terminated character arrays, like "string" or

char s[]={'s','t','r','i','n','g',0};

'2' is a single character.

if(!strcmp('2', Key_pressed))

To compare single characters, the following is acceptable:

if (Key_pressed == '2') do_something();

4 
       Key_pressed = My_Keypad.getKey(); //wait for a key to be input

That function does NOT wait for a key to be input.

Who else's keypad would you be using? Really, now, is it that difficult to come up with reasonable instance names?

5

I'm most grateful for the responses and will do my best to mend the errors of my ways. I've gotta say though that as a non-programmer dad trying to learn how to write arduino code on the QT to help out his kid, the condescending remarks come off as unfairly harsh.

6

The above being said, Im anxious to learn to do things the right way... Can I get a quick summary of at least some of the "many,many errors" in my code? (have already changed the name of my keypad instance!)

7

Please read the posts "How to use this forum - please read" and "Read this before posting a programming question".

8

Can I get a quick summary of at least some of the "many,many errors" in my code?

It's more like one error repeated. strcmp() is used to compare strings, not individual characters.

9

"the condescending remarks come off as unfairly harsh."

I've reviewed the posts, I see nothing condescending at all. Looks like mostly straightforward direction & suggestions to me.

Keep working on your coding, it'll get better with practice.

Moderator.

10

ones or zeros, right or wrong, dont be offended

11

Points well-taken... it was the "Really, now, is it that difficult..." that I guess I over-reacted to.

BTW, substituting the "if (Key_pressed == n)" got rid of the strange behavior I was experiencing... And I've just discovered switch, which has eliminated all those ugly nested if-then-else statements!

Thanks to everyone for the help... I'm sure I'll be back!

12

skitch/case solves a lot of problems when decoding keypad presses, see examples mentioned.
https://www.arduino.cc/en/Reference/SwitchCase