This code gives the wrong output. Why? [closed]

Question

void setup()
{ 
  int calc(9,2);
  Serial.begin(9600);
}

void loop()
{}

int calc(int val1, int val2)
{
  Serial.print(val1 + val2);
}

It's not syntax error, i am getting output as 1, i should get 11.

Answer 1

A function's name should tell what it does.

Something called calc() should not mainly print (except for debug purposes))

void setup() { 
  Serial.begin(9600);
  printSum(9,2);
}
void loop() {}

void printSum(int val1, int val2) {
  Serial.print(val1 + val2);
}

The other good approach is to really define a function returning a result.

int calc(int a, int b) {
   return a+b;
}
void setup() {
   Serial.begin(9600);
   Serial.println(calc(9,2));
}
void loop() {}

Answer 2

If your goal is to call your function with int calc(9,2);, you might want to change it to calc(9,2);, this is the way to call functions, no type declarator needed if you arent creating said function (or in a declaration, wich has nothing to do in the setup) If you want to declare your functions, it must be done at the very top of your code, out of the setup function, and with arduino 1.8.9 on my end, this is not mandatory.

Also, you are calling your printing function before the Serial.begin(), one good practice may be to Serial.begin() at the very top of your setup, so you don't make mistakes on why your debug is not showing.

As on why you have a 1 printed, if that's all your code, i don't really know, i have no output when i try your code on my end

tl;dr;

void setup() {
  Serial.begin(9600);
  calc(9,2);
}