int marks_summation(int* marks, int number_of_students, char gender) {
   int sum=0;
   char g,b;
   for(int i=0;i<number_of_students;i++){
       if(i%2!=0 && gender=='g'){
           sum+=marks[i];
       }
       else if(i%2==0 && gender=='b'){
           sum+=marks[i];
       }
   }
   return sum;
}