Type 2 numbers in serial mon. and it should give me the multiplication of both

Using Arduino Programming Questions
1

Hi i have to make this programm for school but i dont get how to do it.my code looks like this

int a=0;
int b=0;
int erg=0;
void setup(){
  Serial.begin(9600);
  
}
  void loop(){


      if (Serial.available() > 0 && a==0){ 
      a=Serial.read()-48;
      Serial.print("1.number:");
      Serial.println(a,DEC);
     }
 
  if(Serial.available() > 0 && a!=0);{
      b=Serial.read()-48;
      Serial.print("2.number:");
      Serial.println(b,DEC);
  }
 
      if(a!=0 && b!=0){
        erg=a*b;
        Serial.print("answer:");
        Serial.println(erg,DEC);
      } 
     }

but if i start the serial monitor now it only repeats 2.number:-49

2

The semicolon in this line is wrong, it causes the if to be ignored and the block always executes.

if(Serial.available() > 0 && a!=0);{

Remove the ; and see if it works.

3

now it works if i write the 2. number very fast after the first one but if i wait a little bit it says i have typed the 1. again

1.number:4
1.number:2
1.number:1
1.number:1
1.number:2
2.number:3
answer:6
1.number:5
1.number:2
1.number:2
4

Strange. That doesn't happen to me. Did you change anything other than removing the ';' from the second if?

5

Why do you check if a or b == 0 ?
That are valid integers so the challenge is to write code that could multiply those values too!

hint: use a non digit char e.g. space as separator