3. Locations

Traditionally, a text adventure is a virtual world consisting of (many) different locations. Though this is not essential (some adventures take place in a single room!), it is a good way to explain the use of data structures.

We start by defining a struct to represent a location. It contains two simple attributes to start with (more may follow later).

Next, we define an array of locations. For now, we keep it really simple: just two locations.

Using the data from the array is simple. For example, the following line of code will output "You are in an open field."

Let's put this into practice. In the code sample from the previous chapter, we alter lines 3, 26, 30 and 43 (slightly highlighted below).

Explanation:

Line 3: express your intent to use the functions defined in the module below.
Line 26, 30: call the new functions.
Line 43: at the start of the game, describe the player's surroundings, as if the player entered the command 'look around'.

Explanation:

Line 4-11: in C you can use a single statement to define a type (struct location), declare a variable (locs) and fill it with its initial values.
Line 8: the array length (2) is not specified; in this case, the C compiler will automatically determine the length based on the number of elements in the initializer.
Line 13: as variable locs is allocated statically, we can let the compiler calculate the total number of locations; very handy once we start adding more locations. The calculation is rather obscure to look at, so we give it a meaningful name numberOfLocations. The calculation is performed at compile time, not in runtime, so we can use #define without any performance penalty.
Line 15: the player's location is initially 0 (indexing the first array element: the field); change the value of locationOfPlayer to move to a different location (as is done in line 43).
Line 15, 31: because numberOfLocations is an unsigned integer, we use the same type to declare variables locationOfPlayer and i.
Line 44: after the player has moved, the new location is immediately reported back, as if the player entered the command 'look around'.

Now the commands look around and go <location> have really come to life! Feel free to experiment by adding more locations. Of course, the game is still far from perfect. Right now, there is too much freedom: from every location, the player can reach any other location without restrictions. In chapter 6, we will show how to 'connect' locations. But next up, we will start adding objects to the game.

	location.h
1 2	extern void executeLook(const char noun); extern void executeGo(const char noun);
	location.c
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50	#include <stdio.h> #include <string.h> struct location { const char description; const char tag; } locs[] = { {"an open field", "field"}, {"a little cave", "cave"} }; #define numberOfLocations (sizeof(locs) / sizeof(locs)) static unsigned locationOfPlayer = 0; void executeLook(const char noun) { if (noun != NULL && strcmp(noun, "around") == 0) { printf("You are in %s.\n", locs[locationOfPlayer].description); } else { printf("I don't understand what you want to see.\n"); } } void executeGo(const char *noun) { unsigned i; for (i = 0; i < numberOfLocations; i++) { if (noun != NULL && strcmp(noun, locs[i].tag) == 0) { if (i == locationOfPlayer) { printf("You are already there.\n"); } else { printf("OK.\n"); locationOfPlayer = i; executeLook("around"); } return; } } printf("I don't understand where you want to go.\n"); }

How to program a text adventure in C

3. Locations