main.c

#include <stdio.h>

void get_grades(float *sum, int *num, int *passed) {
  // Initialize all values to 0
  (*num) = 0;
  (*passed) = 0;
  (*sum) = 0.0f;
  // Loop through the maximum grades
  for ((*num) = 0; (*num) < 10; (*num)++) {
      // Store for the grade
    float grade;

    // Do forever
    for (;;) {
        // Ask for the grade
      printf("[%02d] Grade: ", (*num) + 1);
      scanf("%f", &grade);

      // If the grade is below 0, stop asking completely
      if (grade < 0.0f) {
        return;
        // If the grade is valid, break out of forever
      } else if (grade >= 1.0f && grade <= 10.0f) {
        break;
      }
    }

    // If the grade is higher than 5.5
    if (grade >= 5.5f) {
        // The student has passed
      (*passed) += 1;
    }

    // Add the grade to the sum
    (*sum) += grade;
  }
}

int main() {
  printf("Please specify the grades between 1.0 and 10, -1 exits\n");

  // Storage for all variables
  int passed = 0;
  int num = 0;
  float sum = 0.0f;

  // Ask for all the grades
  get_grades(&sum, &num, &passed);

  // Check if there is at least one grade, print the results
  if (num > 0) {
    printf("Average: %f\n", sum / (float)(num));
    printf("Passed : %d\n", passed);
  }
  return 0;
}