R conditional loop executes but goes haywire

i am trying to iterate over all the data, depending on the IF statements a new column is created. I do not get an error but the results are completely off. so it is hard for me to find the error. Any tip or suggestion is appreciated

```{r, echo=TRUE}
for (i in 1:length(Data)){
  if (Data$P[i]=="A")
  {
    Data$NC[i]=Data$C[i]*5
  }
  else if (Data$P[i]=="B")
  {
    Data$NC[i]=Data$C[i]*10
  }
  else if (Data$P[i]=='C')
  {
    DataNC[i]=Data$C[i]*15
  }
  else if (Data$P[i]=="D")
  {
    Data$NC[i]=Data$C[i]*20
  }

}