Untitled

uint8_t index=0;
char command=0;
char value[4];
uint8_t avalue=0;

while(index < 3){
  if(Serial.available())
  {
    if(index==0){ // index is 0 so we are hopefully recieving a,b,c....
      command = Serial.read();
    }
    else{ // index is more then 0, we should be recieving the value
      value[index] = Serial.read();
    }
    index++
  }
}
avalue = atoi(value); // convert from ascii to int

switch (command){
  case a:
  analogWrite(A, avalue);
  break;
  case b:
  analogWrite(B, avalue);
  //and so on

}


index=0;