This is my solution, how are things?

vector gradingStudents(vector grades) { for(int i = 0; i < grades.size(); i++){

if(grades[i] > 37){
  if((grades[i]+1)%5 == 0)
    grades[i] += 1;
  else if((grades[i]+2)%5 == 0)
    grades[i] += 2;    
}

} return grades; }