Click here to download getgrade.c.

#include <stdio.h>
#include <stdlib.h>

int main() {
  // open file
  FILE* gfile = fopen("grades.txt", "r");

  // read in number of students and number of homeworks
  int students;
  int hws;
  fscanf(gfile, " %i students %i hws", &students, &hws);

  // create 2D array
  int** grades = calloc(students, sizeof(int*));
  for (int i=0; i < students; ++i) {
    grades[i] = calloc(hws, sizeof(int));
  }

  // read in grades from file
  for (int i=0; i < students; ++i) {
    for (int j=0; j < hws; ++j) {
      fscanf(gfile, " %i", &grades[i][j]);
    }
  }

  // lookup grades
  int stlookup;
  printf("Which student (-1 to quit)? ");
  fflush(stdout);
  scanf(" %i", &stlookup);

  while (stlookup >= 0) {
    int hwlookup;
    printf("Which homework? ");
    fflush(stdout);
    scanf(" %i", &hwlookup);

    if (stlookup >= 1 && stlookup <= students
        && hwlookup >= 1 && hwlookup <= hws)
    {
      // note: subtract 1 to do 0-based indexing
      int stgrade = grades[stlookup-1][hwlookup-1];
      printf("Student %i's grade on homework %i is %i\n",
             stlookup, hwlookup, stgrade);
    } else {
      printf("ERROR: Invalid student or HW index.\n");
    }

    printf("Which student (-1 to quit)? ");
    fflush(stdout);
    scanf(" %i", &stlookup);
  }

  // clean-up
  for (int i=0; i < students; ++i) {
    free(grades[i]);
  }
  free(grades);
  fclose(gfile);

  return 0;
}