Why is IF statement executing on itself

Question

x = 5;
Serial.println (x);
if (x == 0);
 {
 //stuff in this IF keeps happening why ?
 //Iam too stupid ?
 }

• Juraj: the if statement must be executed to evaluate the condition. if the condition is true the following command or block of commands is executed. your command after the if is ; (empty command)

Answer 1

You have a rogue semi-colon.

Splitting your code up on the end of statements you get:

1. x = 5; 
2. Serial.println (x);
3. if (x == 0);
4. { // stuff }

With the semi-colon after the if it terminates the if before the opening block {, and that block becomes a completely separate statement detached from the if.

• Duncan C: Yeah, most of us have been bitten by this one. I wish C/C++ compilers would flag this if (condition); form with a warning as it is very likely a mistake, and is certainly bad coding practice even if intentional. (Same for if (a=b). Valid, but bad practice.)
• Majenko: @DuncanC They can. GCC has the flag -Wempty-body: "Warn if an empty body occurs in an "if", "else" or "do while" statement. This warning is also enabled by -Wextra."
• Duncan C: It should be on by default.
• Duncan C: Hell, I'd even argue it should be flagged as an error. Anybody who deliberately writes a "side-effect only" if statement should be shot. :)
• Majenko: You can turn it on in preferences in the Aduino IDE. /home/matt/Arduino/sketch_mar30a/sketch_mar30a.ino:5:14: warning: suggest braces around empty body in an 'if' statement [-Wempty-body]