#include <stdio.h>

/* Prototype */
char letterGrade(float score); 

int main() {
   /* providing values for s1 and s2 */
   /* to see what happens when not enough */
   /* values are provided by user */
   float s1 = 77, s2 = 88, avg;
   int valuesRead;

   printf("Enter two scores using <score1> and <score2> format: ");
   valuesRead = scanf("%f and %f", &s1, &s2);
   printf("The number of values read is %d\n", valuesRead);

   avg = (s1 + s2) / 2;
   printf("Average for %f and %f is %.2f\n", s1, s2, avg);

   printf("Your letter grade is %c\n", letterGrade(avg));

   return 0;
}

char letterGrade(float score) {
   if (score >= 90) {
      return 'A';
   } else if (score >= 80) {
      return 'B';
   } else {
      return 'F';
   }
}