'else' without previous 'if ' ---- I am getting this error, suggestions pls

Other Hardware LEDs and Multiplexing
1 
const int xpin = A0;
const int ypin = A1;
const int zpin = A2;
const int led1 = 5;
const int led2 = 6;
const int led3 = 7;

void setup() 
{
  Serial.begin(9600);
  pinMode(led1,OUTPUT);
  pinMode(led2,OUTPUT);
  pinMode(led3,OUTPUT);
}
unsigned int zaxis,yaxis,xaxis;
void loop()
{
  xaxis = analogRead(xpin);
  yaxis = analogRead(ypin);
  zaxis = analogRead(zpin);
  if (xaxis > 390);
  {
   digitalWrite (led1,HIGH);
  }
  else
  {
   digitalWrite (led1,LOW);
  }
  if (yaxis > 390);
  {
   digitalWrite (led2,HIGH);
  }
  else
  {
   digitalWrite (led2,LOW);
  }
  if (zaxis > 390);
  {
   digitalWrite (led3,HIGH);
  }
  else
  {
   digitalWrite (led3,LOW);
  }
}
2

Oops.

Every single "if"

3

Remove the semicolons from your if statements.
C

1 Like
4

Welcome to the forum

Delete the semicolons on the end of the if statements. They should not be there

1 Like
5

This worked

6

Do you understand why ?

7

Many Thanks

8 
unsigned int zaxis,yaxis,xaxis;

With the code as it looks, there is no reason for these variables to have global scope.

9

Yea, I removed semicolons from all "if" statements

10

Ah, okay

11

But do you understand what the problem was and why removing the semicolons fixed it ?

12

Can u pls explain ?

13

The structure of an if/else is

if (this is true)
{
  //execute this code
}
else
{
  //execute this code
}

When you put a semicolon on the end of an if test it is the code that is executed when the test returns true so the code effectively becomes

if (this is true)
{
  //execute the semicolon
}
{
  //execute this code
}
else
{
  //execute this code
}

Note how there are now 2 code blocks after the if before the else hence the "else without previous if error

1 Like
14

Ahh.. Got it Now!!
Many thanks for this explanation

15

It is quite a common error, hence the quick responses here

At least when you do it with if/else you get an explicit error when compiling. When you do it with a simple if (or while) the problem can be more difficult to track down because instead of an error the code does not do what you want or expect

16

Yea, Alright

17

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