int marks_summation(int* marks, int number_of_students, char gender) {
  int boys_marks = 0, girls_marks = 0;
  if (gender == 'b') {
    for (int i = 0; i < number_of_students; i+=2) {
        boys_marks += marks[i];
    }
  }else{
    for (int i = 1; i < number_of_students; i+=2) {
        girls_marks += marks[i];
    }
  }
  
  return (gender == 'b')? boys_marks: girls_marks;
}