Malloc + structs

Goals

Note: The next few assignments will be based on this one.

Overview

Scenario: Your team will soon choose a leader. You will be given a list of names and a separate list of each person's "favorite" person on the team. You must create software that can calculate the new leader.

Warm-up exercises

This assignment includes a warm-up exercise to help you get ready. This accounts for 10% of your score for HW07. Scoring will be relatively light, but the usual base requirements apply.

To get the starter files, type this: 264get hw07

For the warm-up, you will create a struct type for a name (first and last). Your type will be called struct Name and it will have two members: first (a char*) and last (a char*). Next, you will create two swap functions: swap_first_last(…) swaps the first and last name in a given struct Name instance. swap_names(…) swaps two struct Name instances using pass-by-address.

In warmup.c, you must replace every /* TODO */ comment with code. The only output is as shown. Fill in the rest of the code to make it work.

Doing the assignment

Here is the overview of what you are creating. (Some specifics have been moved to Requirements.)

• team.h
  • struct Person type definition with at least two fields: name (string), favorite (the person's favorite)
  • struct Team type definition with at least two fields: people (array of struct Person objects) and population (number of people on the team)
  • forward declarations
• team.c
  • create team(int population, char✶ names[], int✶ favorites) creates an instance of struct Team with population people. The favorite of the person named names[i] is favorites[i].
  • pick leader(struct Team✶ team) returns the most popular person, i.e., the person who is the favorite of the greatest number of people.
  • free team(struct Team✶ team) frees all heap memory referred to by the team (directly or indirectly).
• test_team.c
  • main(int argc, char✶ argv[]) function tests your functions in team.c.

Note: Type the declarations into your file manually. Do not copy-paste. (You learn more from typing code manually.)

When you are finished, it will look like this.

Requirements

How much work is this?

This assignment is difficult. It won't require a lot of code, but expect to spend some time debugging and understanding the concepts.

Q&A

1. What is a forward declaration?
   A forward declaration is just the top line of a function definition, which specifies its signature. Examples can be found in your textbook on page 155 (Figure 4-5) and page 165 (Figure 4-12).
   
   For example, in HW04, if you wanted to put everying in one file, you could do so like this. The forward declarations let the compiler know what is coming, even before it has read the full function definition.
   

   void mintf(int n, int radix, char* prefix);    // <--- forward declaration
   void print_integer(const char* format, ...);   // <--- (aka "function declaration")
   
   // Test code
   int main(int argc, char* argv[]) {
     // […]
   }
   
   void print_integer(const char* format, ...) {  // <--- function definition
     // […]
   }
   
   void mintf(int n, int radix, char* prefix) {   // <--- function definition
     // […]
   }
   

2. Why must the struct Person objects be on the heap?
   You don't know in advance (i.e., at compile time) how many you will need.
3. Why must the name field of each struct Person be on the heap?
   The string that was passed to create_team(…) might not exist later.
4. What is the form of the team returned by create_team(…)?
   The structure created by the example in the screenshot will look like this:
   

Updates

9/25: Corrected filename test_team.c (not teamtest.c).

9/26: Clarified where person name should reside, and how population==0 should be handled; added diagram; corrected return type of print_name(…) in warmup.c; moved most specification details to the Requirements table and elaborated on some items.

9/28: NULL and assert(…) are allowed.