Newbie programmer here, and I needed to convert a character to an integer. After some googling, there are 2 main ways to do it (without making it a string first): subtracting by '0' and using atoi(). I understand how to use them and when, but I still don't have the faintist idea as to why they work the way they do. Subtracting by '0' destroys what little understanding I had of concatination, and the name choice of "atoi" baffles me. At first I thought it was shorthand of saying "__ to integer", but what does the 'a' mean??? And how is atoi any different from the mind-breaking char - '0''? So many questions...
So if I passed something like a char array to it, could also work? Nice
Ahhh, that makes sense. Sometimes it's easy to forget that chars are just numbers on a lookup table. Thanks man! I didn't think anyone would replay mere seconds after I asked my question
1. If you enter 1234 in the InputBox of the Serial Monitor (Fig-1) with Newline option and click on the Send Button, then the following data bytes (the ASCII codes for 1, 2, 3, 4, and Newline, Fig-2) are transmitted one-after-another as 10-bit frame (Fig-3) towards the UNO:
0x31 0x32 0x33 0x34 0x0A //the space for clarity and 0x for base
2. The UNO receives all the bytes of Step-1 and saves them in the unseen Serial Buffer. (The byte m = Serial.readBytesUntil('\n', myData, size of myData - 1); code can be used to transfer the data bytes of the Serial Buffer except the Newline character into a char-type user array, char myData[10].)
3. How to reconstruct/retrive the orginal decimal number (1234) from the ASCII elements of the array of Step-2?
4. There are two ways to answer the question of Step-3.
(1) Use atoi() (ASCII to decimal Integer number) function which requires that the last element of the user array of Step-2 must have a null-character (0x00 = '\0').
myData[4] = '\0'; insert null-charcter
int y = atoi(myData);
Serial.print(y, DEC); shows: 1234
(2) Use of Manual Appproach
(a) Extractt 1 from 0x31 which is the item-0 of myData[] array.
byte y0 = myData[0] - '0'
==> byte y0 = 0x31 - 0x30 //see Fig-2
==> byte y0 = 0x01
(b) Similarly, extract y1 = 0x02, y2 = 0x03, and y3 = 0x04 from the remainging items of the array.
(c) Now, perform SHFIT and OR/AND operatons on y0, y1, y2, and y3 to get: y = 1234.
//------------------------------------------------------------------------------------------------------------
Figure-1:
Figure-2:
Figure-3:
Remember that atoi() (ascii to integer) requires a cString as an input so you need a null termination in your char array.
Subtracting '0' to a char works not really because it’s ASCII encoding but more importantly because digits are coded from '0' to '9' successively/contiguously. If they had been arranged in another way in the table then it would not work.
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Misleading our newbie. The Uno received the 0x0A. The method used in your code example to extract the characters from the buffer discarded the 0x0A. From Reference for Serial.readBytesUntil():
The terminator character is discarded from the serial buffer, unless the number of characters read and copied into the buffer equals
length.
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I am editing my post #6.
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This is what I have thought to get the image 1234 on the Serial Monitor:
void setup()
{
Serial.begin(9600);
//---Given--------
byte y0 = 0x01; //00000001
byte y1 = 0x02; //00000010
byte y2 = 0x03; //00000011
byte y3 = 0x04; //00001000
//-----------------------
byte y0y1 = (y0 << 4) | y1; //yoy1 = 00010010
byte y2y3 = (y2 << 4) | y3; //y2y3 = 00100011
//-------------------------------------------
int y = (int)(y0y1 << 8)|(int)y2y3; //y = 00010010 00100011
Serial.print(y, HEX); //shows: 1234
}
void loop()
{
}
Output:
1234
In the Forum -- not everything always comes meaningful! It took centuries for the history of science to get rid of the mythologies that it contained in the name of science?
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