Click here to download sortnames.c.

/**************************************
This program simply reads 10 names from
the file names.txt and prints them out
in alphabetical order by last name, with
ties broken by first name.
**************************************/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

/**************************************
 ** PROTOTYPES
 **************************************/
void selectionSort(char*** data, int size);
int before(char** a, char** b);
int indexOfMax(char*** data, int size);

/**************************************
 ** MAIN FUNCTION
 **************************************/
int main() {
  // Open file names.txt containing 10 names
  FILE* fin = fopen("names.txt", "r");

  // Create and populate 2D array of 10 names
  // names[i][0] is first name
  // names[i][1] is last name
  int size = 10;
  char*** names = calloc(size, sizeof(char**));
  for (int i=0; i < size; ++i) {
    names[i] = calloc(2, sizeof(char*));
    names[i][0] = calloc(128, sizeof(char));
    names[i][1] = calloc(128, sizeof(char));
  }
  for (int i=0; i < size; ++i) {
    fscanf(fin, " %s %s", names[i][0], names[i][1]);
  }

  // Sort!
  selectionSort(names, size);

  // Print in sorted order
  for (int i=0; i < size; ++i) {
    printf("%s %s\n", names[i][0], names[i][1]);
  }

  // clean up
  fclose(fin);
  for (int i=0; i < size; ++i) {
    free(names[i][0]);
    free(names[i][1]);
    free(names[i]);
  }
  free(names);

  return 0;
}

/**************************************
 ** FUNCTION DEFINITIONS
 **************************************/

int before(char** a, char** b) {
  int lastcmp = strcmp(a[1], b[1]);
  if (lastcmp == 0) {
    /* compare first names if last names are equal */
    return strcmp(a[0], b[0]) < 0;
  } else {
    return lastcmp < 0;
  }
}

int indexOfMax(char*** data, int size) {
  int imax = 0, i;
  for(i = 1; i < size; ++i) {
    if (before(data[imax], data[i])) {
      imax = i;
    }
  }
  return imax;
}

void selectionSort(char*** data, int size) {
  for(int length = size; length > 1; --length) {
    int imax = indexOfMax(data, length);
    char** temp = data[length-1];
    data[length-1] = data[imax];
    data[imax] = temp;
  }
}