[SOLVED]Getting #elif compilation error

Projects Programming
1

I want to make a choice between a 16x2 or a 20x4 LCD Display.
Therefore I wrote this :slight_smile:

#ifndef LCD20
  const uint8_t cols = 16;  // 16 for 1602 display, 20 for 2004 display's
  const uint8_t rows = 2;   // 16 for 1602 display, 20 for 2004 display's
#elif
  const uint8_t cols = 20;  // 16 for 1602 display, 20 for 2004 display's
  const uint8_t rows = 4;
#endif

but I get a compilation error:
Compilation error: #elif with no expression
What expression must #elif have to work??

2

Compiles OK for me with a Nano classic as the target board

Which Arduino board and IDE version are you using ?

Please post a complete sketch that illustrates the problem and post the full error message produced by that sketch

3

Given the snippet posted presumably #else is a more reasonable choice.

4

#elif is short for "else if", so it expects an expression to evaluate for the "if" condition.

5

Try again with LCD20 defined, if that is not defined the compiler apparently never processes the #elif.

6

Try lihe this:

#ifndef LCD20
  const uint8_t cols = 16;  // 16 for 1602 display, 20 for 2004 display's
  const uint8_t rows = 2;   // 16 for 1602 display, 20 for 2004 display's
#elif LCDXX
  const uint8_t cols = 20;  // 16 for 1602 display, 20 for 2004 display's
  const uint8_t rows = 4;
#endif

Ref: Preprocessor directives | Microsoft Learn

7

As has been pointed out, the #elif is wrong and should probably be #else so no surprise that compilation fails under some circumstances

1 Like
8

So changed the #elif To #else and it compiles correct, full code

#include <Wire.h>
#define LCD20 false        // system uses 20X4 LCD else a 16x2 LCD display
#ifndef LCD20
  const uint8_t cols = 16;  // 16 for 1602 display, 20 for 2004 display's
  const uint8_t rows = 2;   // 16 for 1602 display, 20 for 2004 display's
#else
  const uint8_t cols = 20;  // 16 for 1602 display, 20 for 2004 display's
  const uint8_t rows = 4;
#endif

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);

  value = millis();
  Serial.println(value);
  Serial.println(rows);
  }
void loop() {}

But now if #define LCD20 false or true in boht cases the value of rows = 4

9

In both cases of LCD20 being true or false, LCD20 is being defined. Therefore, the #else path is always taken.

Comment out the #define of LCD20, and then the #ifndef path should be taken.

10

So I have rewritten this section to

#define LCD20 false  // system uses 20X4 LCD else a 16x2 LCD display
#if LCD20
const uint8_t cols = 20;  // 16 for 1602 display, 20 for 2004 display's
const uint8_t rows = 4;
#else
const uint8_t cols = 16;  // 16 for 1602 display, 20 for 2004 display's
const uint8_t rows = 2;   // 16 for 1602 display, 20 for 2004 display's
#endif
LiquidCrystal_I2C lcd(0x27, cols, rows);  // set the LCD address to 0x27 for a 16 chars and 2 line display

Thnx for the input

11

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