CONTENTS
1. Introduction
2. The main loop
3. Locations
4. Objects
5. Inventory
6. Passages
7. Distance
8. North, east, south, west
9. Code generation
10. More attributes
11. Conditions
12. Open and close
13. The parser

How to program a text adventure in C

2. The main loop

Let's bring some basic interaction into our program!

The basic principle of a text adventure is simple:

  1. The player enters a command.
  2. The program parses and executes the command.
  3. Repeat steps 1 and 2 until the player decides to quit.
The code sample below consists of three functions, one for each step:
  1. function getInput
  2. function parseAndExecute
  3. function main takes care of calling the other two functions repeatedly

This program, however short it may be, already responds to commands like look around, go north and quit. But of course, it is not much of a game. It has no locations, no items; all there is, is darkness. So in the next chapter, we will begin adding locations.

Sample output
Welcome to Little Cave Adventure. It's very dark in here. --> look around It's too dark to see. --> go north It's too dark to go anywhere. --> eat sandwich I don't know how to 'eat'. --> quit Bye!
main.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 #include <stdio.h> #include <string.h> static char input[100]; static int getInput() { printf("\n--> "); return fgets(input, sizeof(input), stdin) != NULL; } static int parseAndExecute() { char *verb = strtok(input, " \n"); char *noun = strtok(NULL, " \n"); if (verb != NULL) { if (strcmp(verb, "quit") == 0) { return 0; } else if (strcmp(verb, "look") == 0) { printf("It's too dark to see.\n"); } else if (strcmp(verb, "go") == 0) { printf("It's too dark to go anywhere.\n"); } else { printf("I don't know how to '%s'.\n", verb); } } return 1; } int main() { printf("Welcome to Little Cave Adventure.\n"); printf("It's very dark in here.\n"); while (getInput() && parseAndExecute()); printf("\nBye!\n"); return 0; }

Explanation:

Notice our program stops at nothing but a command from the player (either quit or end-of-file). So what about ‘game over’ situations, i.e. death and victory? Well, those are conditions that might end the game, but not necessarily end the program.

There is also a practical problem with terminating the program without the player's consent: in a windowing system, it is not unlikely for a text-based program to be running in an application window that immediately closes when the program ends, even before the player has had a chance to read the final message. We could delay this effect with “press any key to exit” or “wanna quit (y/n)”, but why bother when there is already a perfectly sane alternative? Just let the player type in ‘quit’ whenever he is ready to leave the imaginary world behind.

Naturally, all this is just an advice; you can take it or leave it. That's the great thing about writing an adventure in a general-purpose language: you can craft it any way you like.

Next chapter: 3. Locations