is arduino have syntax to convert from char to number type?

Projects Programming
1

hi sorry for my bad english,
i trying to create number input like calculator,
example =
if i press in keypad button "1", then i press keypad button "2" then the result is 12(twelve),
then if i press keypad button "3", the result is 123(one hundred twenty-three),,,etc

but my problem is converting from char type to int type,
i google it for a hour and found nothing that i looking for,
i found about .atoi and int(), but the result is wrong

this is code if it can help :

#include <Wire.h>
#include <Keypad.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);
int led_pin = 13;
const byte ROWS = 4; //four rows
const byte COLS = 4; //four columns
//define the cymbols on the buttons of the keypads
char hexaKeys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};
byte rowPins[ROWS] = {4, 5, 6, 7}; //connect to the row pinouts of the keypad
byte colPins[COLS] = {8, 9, 10, 11}; //connect to the column pinouts of the keypad

//initialize an instance of class NewKeypad
Keypad customKeypad = Keypad( makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS);

char customKey;
long int Value = 0;
long int TempValue = 0;

void setup() {
  // put your setup code here, to run once:
  Serial.begin (9600);
  lcd.begin(16, 2);
  lcd.clear();
  lcd.print("LCD");
  lcd.setCursor(1, 1);
  lcd.print("TEST");
}

void loop() {

  // put your main code here, to run repeatedly:
  char customKey = customKeypad.getKey();
  if (customKey) {
    lcd.clear();
    Serial.print(" and button pushed is: ");
    Serial.println(customKey);
    lcd.setCursor(0, 0);
    lcd.print(customKey);
    //TempValue = ConvertCharToInt(customKey); [color=red]<= this is the problem[/color]
    Value = (Value * 10) + TempValue;
    lcd.setCursor(0, 1);
    lcd.print(Value);
    Serial.println(TempValue);
  }
}

can somebody help me with the syntax please!!

2

Subtract '0' from the character returned by getKey() and you will have the actual digit instead of a character representing it.

3

UKHeliBob:
Subtract '0' from the character returned by getKey() and you will have the actual digit instead of a character representing it.

thanks for the reply,
but how you subtract?
customKey-0?

4

You subtract '0' from customKey, not 0. Spot the difference.

'0' is ASCII 48 (decimal)
'7' (for instance) is ASCII 55 (decimal)

So if you do

digit = customKey - '0';

when customKey is '7' (ie 55) the result will be
digit = 55 - 48which gives 7

Try some example on paper and it should become clear

5

UKHeliBob:
You subtract '0' from customKey, not 0. Spot the difference.

'0' is ASCII 48 (decimal)
'7' (for instance) is ASCII 55 (decimal)

So if you do

digit = customKey - '0';

when customKey is '7' (ie 55) the result will be
digit = 55 - 48which gives 7

Try some example on paper and it should become clear

thank you thank you, it works, ha ha ha ha ha ha

6

I'm glad it works.

Of course you could subtract 48 instead of '0' if that makes more sense