Click here to download pickteams.c.

/************************************************
This program is a simple application of 2D arrays.
The purpose is to take a list of people, and randomly
create teams from them.  The names come from a
file names.txt.
*************************************************/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <time.h>

/************************************************
 ** PROTOTYPES
 ************************************************/
char** readnames(int* numptr);
char** makearray(int size);
void freearray(char** arr, int size);

/************************************************
 ** MAIN FUNCTION
 ************************************************/
int main() {
  // seed the random number generator differently on each run
  srand(time(0));

  // Read file of names
  int np;
  char** names = readnames(&np);

  // Get number of teams from user
  int nt;
  printf("There are %i people.\n", np);
  printf("How many teams would you like? (make it evenly divide n) ");
  fflush(stdout);
  scanf(" %i", &nt);
  if (np % nt != 0) {
    printf("ERROR: Number of teams must evenly divide number of people\n");
    return 1;
  }

  // Allocate array of teams
  int teamSize = np / nt;
  char*** teams = calloc(nt, sizeof(char**));
  for (int i = 0; i < nt; ++i) {
    teams[i] = makearray(teamSize);
  }

  // dole out people to teams
  int npremaining = np;
  for(int i = 0; i < teamSize; ++i) {
    for(int it = 0; it < nt; ++it) {
      int inext = rand() % npremaining;
      // copy next name to their team
      strcpy(teams[it][i], names[inext]);
      // effectively shrink size of names array by copying the
      // last remaining name to the place we just copied from
      --npremaining;
      if (inext < npremaining) {
        strcpy(names[inext], names[npremaining]);
      }
    }
  }

  // print teams
  for(int it = 0; it < nt; ++it) {
    printf("Team %i:", it+1);
    for (int i=0; i < teamSize; ++i) {
      printf(" %s", teams[it][i]);
    }
    printf("\n");
  }

  // clean-up
  freearray(names, np);
  for (int i=0; i < nt; ++i) {
    freearray(teams[i], teamSize);
  }
  free(teams);

  return 0;
}

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

// reads names from "names.txt" and returns an array of
// strings for each name. Also assigns the number of names
// to the int that numptr points to.
char** readnames(int* numptr) {
  FILE* fin = fopen("names.txt", "r");
  fscanf(fin, " N = %i", numptr);
  char** result = makearray(*numptr);

  for (int i=0; i < *numptr; ++i) {
    fscanf(fin, " %s", result[i]);
  }

  fclose(fin);
  return result;
}

// allocates an array of that many size-128 strings
char** makearray(int size) {
  char** result = calloc(size, sizeof(char*));
  for (int i=0; i < size; ++i) {
    result[i] = calloc(128, sizeof(char));
  }
  return result;
}

// de-allocates an array of strings
void freearray(char** arr, int size) {
  for (int i=0; i < size; ++i) {
    free(arr[i]);
  }
  free(arr);
}