Arduino程序Bug排查：lowConc与highConc值为何被重置为0？

问题根源 #

你代码中的Abs、Conc1至Conc6是全局变量，它们的初始化逻辑在程序启动阶段（setup()执行前）就会运行。此时lowConc和hiConc的默认值为0，导致这些计算变量被初始化为0。后续通过键盘输入更新lowConc和hiConc后，这些变量不会自动重新计算——全局变量的初始化只会执行一次。

手动赋值测试正常是因为你直接在全局变量定义时给lowConc/hiConc赋值，初始化阶段就能得到正确的计算结果。

修复方案 #

将浓度计算逻辑移到获取完lowConc和hiConc之后执行，确保每次输入新值后都重新计算校准浓度。可以把计算逻辑封装成一个函数，在确认完最高浓度后调用。

修正后的完整代码 #

//SDA to Pin A4
//SCL to Pin A5

#include <Keypad.h>
#include <LCD_I2C.h>

//_Declaration_
//Display
LCD_I2C lcd(0x27, 16, 2);
//Keypad
const int ROW_NUM = 4; //four rows
const int COLUMN_NUM = 4; //three columns
char keys[ROW_NUM][COLUMN_NUM] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6' ,'B'},
  {'7', '8', '9' ,'C'},
  {'*', '0', '#', '.'}
};

byte pin_rows[ROW_NUM] = {9, 8, 7, 6};   //connect to the row pinouts of the keypad
byte pin_column[COLUMN_NUM] = {5, 4, 3, 2}; //connect to the column pinouts of the keypad

Keypad keypad = Keypad( makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM );

//*Variables
//Keypad
String inputString; //Working memory
long inputInt; //long term memory

byte whileloop = 0; //to keep while loops running

//User input number pad
float lowConc; // Memory of the lowest Concentration
float hiConc; // Memory of the highest Concentration

// Calculated distances between lowConc and highConc to make 6 Measurements
float Abs;
//Concentration of the Calibrationsolutions
float Conc1, Conc2, Conc3, Conc4, Conc5, Conc6;

//Textbloecke
String low = "lowest";
String hi = "highest";

// 新增计算校准浓度的函数
void calculateCalibrationConcs() {
  Abs = (hiConc - lowConc)/5;
  Conc1 = lowConc;
  Conc2 = lowConc + Abs;
  Conc3 = Conc2 + Abs;
  Conc4 = Conc3 + Abs;
  Conc5 = Conc4 + Abs;
  Conc6 = Conc5 + Abs;
}

void setup() {
  lcd.begin();
  lcd.backlight();
  inputString.reserve(10); // maximum number of digit for a number is 10, change if needed
}

//Programming blocks
void dcd (int a, int b) //Code block to delay, clear display and delay again
{   
  delay(a);
  lcd.clear();
  delay(b);
}

void printSolution () //Ausgabe von Text um die berechneten Konzentrationen anzuzeigen
{  
  lcd.setCursor(0, 0); 
  lcd.print("Concentration of");
  lcd.setCursor(0, 1);
  lcd.print("the solutions:");
  dcd(4000, 500);
      
  lcd.print(Conc1);
  dcd(2000, 400);
  lcd.print(Conc2);
  dcd(2000,400);
  lcd.print(Conc3);
  dcd(2000, 400);
  lcd.print(Conc4);
  dcd(2000,400);
  lcd.print(Conc5);
  dcd(2000, 400);
  lcd.print(Conc6);
  dcd(2000,400);
}

void cursor0 ()
{
  lcd.setCursor(0, 0);
}

// 补充缺失的printinputConc函数
void printinputConc(String type) {
  lcd.clear();
  cursor0();
  lcd.print("Insert " + type);
  lcd.setCursor(0, 1);
  lcd.print("concentration:");
}

void loop() {
Insert_lowest_Concentration:
  
  printinputConc(low);                                   //"insert lowest concentration"
  while (lowConc == 0) {
    char key = keypad.getKey();

    if (key) {
      lcd.print(key);

      if (key >= '0' && key <= '9') {     // only act on numeric keys
        inputString += key;               // append new character to input string
        lcd.clear();
        cursor0();
        lcd.print(inputString);
      }
      else if (key == '#')
      {
        if (inputString.length() > 0)
        {
          lowConc = inputString.toFloat(); // 改用toFloat支持小数输入
          lcd.clear();               // clear screen
          inputString = "";
        }
      }
      else if (key == '*')
      {
        inputString = "";            // clear input
        lcd.clear();               // clear screen
      }
      else if (key == '.')
      {
        inputString += key;               // append new character to input string
        lcd.clear();
        cursor0();
        lcd.print(inputString);  
      }
    }
  }

  lcd.clear();
  cursor0();
  lcd.print(lowConc);
  lcd.setCursor(0, 1);
  lcd.print("Confirm?");

  while (whileloop == 0) {
    char key = keypad.getKey();

    if (key) {
      if  (key == '#') {
        break;
      }
      else if (key == '*') {
        lowConc = 0; // 重置变量以便重新输入
        lcd.clear();               
        goto Insert_lowest_Concentration;
      }
    }
  }

Insert_highest_Concentration:
  printinputConc(hi);                                 //"insert highest concentration"
  while (hiConc == 0) {
    char key = keypad.getKey();

    if (key) {
      lcd.print(key);

      if (key >= '0' && key <= '9') {     // only act on numeric keys
        inputString += key;               // append new character to input string
        lcd.clear();
        cursor0();
        lcd.print(inputString);
      }
      else if (key == '#')
      {
        if (inputString.length() > 0)
        {
          hiConc = inputString.toFloat(); // 改用toFloat支持小数输入
          lcd.clear();               // clear screen
          inputString = "";
        }
      }
      else if (key == '*')
      {
        inputString = "";            // clear input
        lcd.clear();               // clear screen
      }
      else if (key == '.')
      {
        inputString += key;               // append new character to input string
        lcd.clear();
        cursor0();
        lcd.print(inputString);  
      }
    }
  }
 
  lcd.clear();
  cursor0();
  lcd.print(hiConc);
  lcd.setCursor(0, 1);
  lcd.print("Confirm?");

  while (whileloop == 0) {
    char key = keypad.getKey();

    if (key) {
      if  (key == '#') {
        break;
      }
      else if (key == '*') {
        hiConc = 0; // 重置变量以便重新输入
        lcd.clear();               
        goto Insert_highest_Concentration;
      }
    }
  }

  // 输入完成后计算校准浓度
  calculateCalibrationConcs();
  printSolution();                                     //输出计算后的浓度值

  lcd.clear();
  cursor0();
  lcd.print("Start filling?");

  while (whileloop == 0) {
    char key = keypad.getKey();

    if (key) {
      if  (key == '#') {
        break;
      }
      else if (key == '*') {
        inputString = "";
        lowConc = 0;
        hiConc = 0;
        lcd.clear();               
        goto Insert_lowest_Concentration;
      }
    }
  }
}

额外优化点：

• 补充了缺失的printinputConc函数（原代码中调用但未定义）
• 将toInt()改为toFloat()，支持小数浓度输入
• 在重新输入时重置lowConc/hiConc为0，避免循环条件失效

内容的提问来源于stack exchange，提问作者BogBod20