Click here to download stsort.c.

/*********************************************
This program reads in student/grade data from
namedgrades.txt, and prints out student names
and HW#4 scores in order from lowest to highest
score on HW#4.
**********************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/*********************************************
 ** PROTOTYPES & STRUCT DEFINITIONS
 *********************************************/
struct student {
  int* hw;
  char name[128];
};

void sort(struct student* data, int size);
int before(struct student a, struct student b);


/*********************************************
 ** MAIN FUNCTION
 *********************************************/
int main() {
  // Open file and read header info
  int numstu, numhw;
  FILE* fin = fopen("namedgrades.txt", "r");
  fscanf(fin, " %i students %i homeworks", &numstu, &numhw);

  // Create array of numstu students with numhw grades each
  struct student* stu = calloc(numstu, sizeof(struct student));
  for(int i = 0; i < numstu; i++) {
    stu[i].hw = calloc(numhw, sizeof(int));
  }

  // Read and store student names and grades
  for(int i = 0; i < numstu; i++) {
    fscanf(fin, " %s", stu[i].name);
    for(int j = 0; j < numhw; j++) {
      fscanf(fin, " %i", &stu[i].hw[j]);
    }
  }

  // SORT!
  sort(stu, numstu);

  // Write out student records
  for(int i = 0; i < numstu; ++i) {
    printf("%s got a %i on HW #4\n", stu[i].name, stu[i].hw[4]);
  }

  // clean up
  fclose(fin);
  for (int i=0; i < numstu; ++i) {
    free(stu[i].hw);
  }
  free(stu);

  return 0;
}

/*********************************************
 ** FUNCTION DEFINITIONS
 *********************************************/
// Determines whether student a comes before b
// when ordered by increasing score on HW #4.
int before(struct student a, struct student b) {
  return a.hw[4] < b.hw[4];
}

// THE USUAL SORTING STUFF!!
void sort(struct student* data, int size) {
  for(int length = size; length > 1; --length) {
    // Find imax, the index of the largest
    int imax = 0;
    for(int i = 1; i < length; ++i) {
      if (before(data[imax], data[i])) {
        imax = i;
      }
    }
    // Swap data[imax] & the last element
    struct student temp = data[imax];
    data[imax] = data[length - 1];
    data[length - 1] = temp;
  }
}