Boolean Logic With Chars For Motor Input Selection

Question

Context of the code:

I am trying to control 2 DC motors through an H-gate, this means there are 4 inputs in total: For DC motor 1: Input 1 (VCC) and Input 2 (GND). For DC motor 2: Input 3(VCC) and Input 2 (GND).

Summary of the code:

The global variables are motinpN which are the pins connected to the different inputs.

An array, which is where the different PWM for the motor speeds are stored.

Char x, which is the variable used for the boolean logic.

Then comes the actual loop which consists of 4 similar functions, the "input selector" function and then the statements that turn the integers stored in the inpSpeedS[] arrays into motor speeds.

The issue:

The code won't enter the first loop, i.e it won't advance past

Serial.println("X equals:"); Serial.print(x);"

I would like to know then, what I am doing wrong in order for this not to work?

 int Speed = 0;
const int motinp1 = 2;
const int motinp2 = 3;
const int motinp3 = 4;
const int motinp4 = 5;
char x = '0';
int inpSpeedS[4]; // An array to determine the speed of each individual input
void setup()
{
 Serial.begin(9600);
 pinMode(motinp1, OUTPUT);
}
void loop() {
 Serial.println("X equals:");
 Serial.print(x);
 if (Serial.available () && (x == '0')) {
 Serial.print("Which input?");
 x = Serial.read();
 Serial.println(x);
 }
 if (Serial.available () && (x == 'a'))
 {
 Serial.println("Input 1 selected");
 inpSpeedS[0] = Serial.parseInt();
 Serial.print("Input 1: ");
 Serial.println(inpSpeedS[0]);
 x = '0'; //reset x, goes back to input selection
 } if (Serial.available () && (x == 'b'))
 {
 Serial.println("Input 2 selected");
 inpSpeedS[1] = Serial.parseInt();
 Serial.print("Input 2: ");
 Serial.println(inpSpeedS[1]);
 x = '0';
 }
 if (Serial.available () && (x == 'c'))
 {
 Serial.println("Input 3 selected");
 inpSpeedS[2] = Serial.parseInt();
 Serial.println("Input 3: ");
 Serial.print(inpSpeedS[2]);
 x = '0';
 }
 if (Serial.available () && (x == 'd'))
 {
 Serial.println("Input 4 selected");
 inpSpeedS[3] = Serial.parseInt();
 Serial.print("Input 4: ");
 Serial.println(inpSpeedS[3]);
 x = '0';
 }
 analogWrite(motinp1, inpSpeedS[0]);
 analogWrite(motinp2, inpSpeedS[1]);
 analogWrite(motinp3, inpSpeedS[2]);
 analogWrite(motinp4, inpSpeedS[3]);
} 

EDIT - I have turned the char 0 from a string literal null to an ASCII code for 0, and same for the other chars. It is still stuck outside of the function loops.

• KIIV: How it's possible that char x = "0"; doesn't yeld on you that you are assigning pointer to C string into char variable?
• GeorgeWTrump: @KIIV I haven't read any books on C yet, only done Udemy courses, so I unfortunately do not know what you're talking about, other than the most superficial I can google myself to in 10 minutes. Could you please elaborate?
• KIIV: There is a huge difference between '0' and "0". First one is ASCII value of character zero, second one is pointer to memory, where the string containing {'0', '0円'} is stored
• Delta_G: Also note you have a shadow x variable in loop. Probably not a good idea.
• Delta_G: Or just lose the "int" in front of x='0'

Answer 1

It's screaming on you:

sketch_jun13a.ino:7:11: warning: invalid conversion from 'const char*' to 'char' [-fpermissive]
 char x = "0";
 ^~~
sketch_jun13a.ino: In function 'void loop()':
sketch_jun13a.ino:21:36: warning: comparison with string literal results in unspecified behavior [-Waddress]
 if (Serial.available () && (x == "0")) {
 ^~~
sketch_jun13a.ino:21:36: warning: ISO C++ forbids comparison between pointer and integer [-fpermissive]
sketch_jun13a.ino:26:36: warning: comparison with string literal results in unspecified behavior [-Waddress]
 if (Serial.available () && (x == "a"))
 ^~~
sketch_jun13a.ino:33:9: warning: invalid conversion from 'const char*' to 'char' [-fpermissive]
 x = "0"; //reset x, goes back to input selection
 ^~~
sketch_jun13a.ino:34:38: warning: comparison with string literal results in unspecified behavior [-Waddress]
 } if (Serial.available () && (x == "b"))
 ^~~
sketch_jun13a.ino:41:9: warning: invalid conversion from 'const char*' to 'char' [-fpermissive]
 x = "0";
 ^~~
sketch_jun13a.ino:43:36: warning: comparison with string literal results in unspecified behavior [-Waddress]
 if (Serial.available () && (x == "c"))
 ^~~
sketch_jun13a.ino:50:9: warning: invalid conversion from 'const char*' to 'char' [-fpermissive]
 x = "0";
 ^~~
sketch_jun13a.ino:52:36: warning: comparison with string literal results in unspecified behavior [-Waddress]
 if (Serial.available () && (x == "d"))
 ^~~
sketch_jun13a.ino:52:36: warning: ISO C++ forbids comparison between pointer and integer [-fpermissive]
sketch_jun13a.ino:58:9: warning: invalid conversion from 'const char*' to 'char' [-fpermissive]
 x = "0";
 ^~~

Basically this is char variable with assigned character literal: char x = '0';

And this is C string: char str[] = "0"; or its equivalent: char str[] = {'0', '0円'};. Where '0円' is so called NUL Terminal character.

Everything about C strings you need to know

EDIT:

Simple demo for the "parser" - it's not perfect but should be enough:

char x = '0';
int inpSpeedS[4]; // An array to determine the speed of each individual input
void setup() {
 Serial.begin(9600);
 Serial.println("Select channel [a..d] and speed [0..255]: ");
}
void loop() {
 if (Serial.available() > 1) { // wait for more characters in buffer
 switch (Serial.read()) {
 case 'a': inpSpeedS[0] = Serial.parseInt(); break;
 case 'b': inpSpeedS[1] = Serial.parseInt(); break;
 case 'c': inpSpeedS[2] = Serial.parseInt(); break;
 case 'd': inpSpeedS[3] = Serial.parseInt(); break;
 default : return; // skip invalid characters like line endings
 }
 Serial.print("Speeds: ");
 for (auto spd : inpSpeedS) {
 Serial.print(' ');
 Serial.print(spd);
 }
 Serial.println();
 Serial.println("Select channel [a..d] and speed [0..255]: ");
 /*
 analogWrite(motinp1, inpSpeedS[0]);
 analogWrite(motinp2, inpSpeedS[1]);
 analogWrite(motinp3, inpSpeedS[2]);
 analogWrite(motinp4, inpSpeedS[3]);
 */
 }
}

And the result:

-> Select channel [a..d] and speed [0..255]:
<- a547
-> Speeds: 547 0 0 0
-> Select channel [a..d] and speed [0..255]:

• GeorgeWTrump: Ah thank you, But by this logic, shouldn't turning [code]char x = "0"[/code] into [code]char x = '0'[/code] then fix the loop? If yes, then something else was also wrong with the loop, since it still is stuck at [code] Serial.println("X Equals:"); Serial.print(x);[/code]
• KIIV: You have to fix all of it including 'a', 'b', 'c', 'd'. But there might be another mistake, as the code cannot be compiled due to missing variables I was lazy to add up
• KIIV: Btw, it's not stucked, if you send for example a154, it'll set the first channel to 154, but it should be set once, you don't want to send it each loop. The same as you don't want to send output every loop interation
• KIIV: @GeorgeWTrump I've added little bit simplified example but somehow working
• KIIV: Let us continue this discussion in chat.