/* * File: teach.c * ------------- * This program executes a simple programmed instruction course. * The course is specified by a data file containing all the * course information.  The data structures and the format of * the data file are described in Chapter 16. */#include <stdio.h>#include <string.h>#include <ctype.h>#include "genlib.h"#include "strlib.h"#include "simpio.h"/* * Constants * --------- * MaxQuestions          -- Maximum question number * MaxLinesPerQuestion   -- Maximum number of lines per question * MaxAnswersPerQuestion -- Maximum answers per question * EndMarker             -- String marking end of question text */#define MaxQuestions          100#define MaxLinesPerQuestion    20#define MaxAnswersPerQuestion  10#define EndMarker "-----"/* Data structures *//* * Type: answerT * ------------- * This structure provides space for each possible answer * to a question. */typedef struct {    string ans;    int nextq;} answerT;/* * Type: questionT * --------------- * This structure provides space for all the information * needed to store one of the individual question records. * Because this structure is large and it makes sense * to refer to it as a single entity, questionT is defined * as a pointer type. */typedef struct {    string qtext[MaxLinesPerQuestion+1];    answerT answers[MaxAnswersPerQuestion];    int nAnswers;} *questionT;/* * Type: courseDB * -------------- * This type is used to define the entire database, which is * a pointer to a record containing the title and an array of * questions. */typedef struct {    string title;    questionT questions[MaxQuestions+1];} *courseDB;/* Private function declarations */static courseDB ReadDataBase(void);static bool ReadOneQuestion(FILE *infile, courseDB course);static void ReadQuestionText(FILE *infile, questionT q);static void ReadAnswers(FILE *infile, questionT q);static FILE *OpenUserFile(string prompt, string mode);static void ProcessCourse(courseDB course);static void AskQuestion(questionT q);static int FindAnswer(string ans, questionT q);/* Main program */main(){    courseDB course;    course = ReadDataBase();    ProcessCourse(course);}/* Section 1 -- Functions to read the data file *//* * Function: ReadDataBase * Usage: ReadDataBase(); * ---------------------- * This function asks the user for a file name and reads * in the database for the course.  The file is formatted * as discussed in the section "Designing the external * structure" in Chapter 16. */static courseDB ReadDataBase(void){    FILE *infile;    courseDB course;    infile = OpenUserFile("Enter name of course: ", "r");    course = New(courseDB);    course->title = ReadLine(infile);    while (ReadOneQuestion(infile, course));    fclose(infile);    return (course);}/* * Function: ReadOneQuestion * Usage: while (ReadOneQuestion(infile, course)); * ----------------------------------------------- * This function reads in a single question from infile into the * course data structure.  As long as the complete question is * read successfully, this function returns TRUE.  When the end * of the file is encountered, the function returns FALSE. * Thus, the "Usage" line above reads the entire data file. */static bool ReadOneQuestion(FILE *infile, courseDB course){    questionT question;    string line;    int qnum;    line = ReadLine(infile);    if (line == NULL) return (FALSE);    qnum = StringToInteger(line);    if (qnum < 1 || qnum > MaxQuestions) {        Error("Question number %d out of range", qnum);    }    question = New(questionT);    ReadQuestionText(infile, question);    ReadAnswers(infile, question);    course->questions[qnum] = question;    return (TRUE);}/* * Function: ReadQuestionText * Usage: ReadQuestionText(infile, question); * ------------------------------------------ * This function reads the text of the question into the * question data structure, which must have been allocated * by the caller.  The end of the question text is signaled * by a line matching the string EndMarker. */static void ReadQuestionText(FILE *infile, questionT q){    string line;    int nlines;    nlines = 0;    while (TRUE) {        line = ReadLine(infile);        if (StringEqual(line, EndMarker)) break;        if (nlines == MaxLinesPerQuestion) {            Error("Too many lines");        }        q->qtext[nlines] = line;        nlines++;    }    q->qtext[nlines] = NULL;}/* * Function: ReadAnswers * Usage: ReadAnswers(infile, question); * ------------------------------------- * This function reads the answer pairs for the question * from the input file.  Each answer consists of a string * followed by a colon, followed by the number of the next * question to be read.  The end of the answer list is * signaled by a blank line or the end of the file. */static void ReadAnswers(FILE *infile, questionT q){    string line, ans;    int len, cpos, nextq, nAnswers;    nAnswers = 0;    while ((line = ReadLine(infile)) != NULL           && (len = StringLength(line)) != 0) {        cpos = FindChar(':', line, 0);        if (cpos == -1) Error("Illegal answer format");        ans = SubString(line, 0, cpos - 1);        nextq = StringToInteger(SubString(line, cpos+1, len-1));        q->answers[nAnswers].ans = ConvertToUpperCase(ans);        q->answers[nAnswers].nextq = nextq;        nAnswers++;    }    q->nAnswers = nAnswers;}/* * Function: OpenUserFile * Usage: fileptr = OpenUserFile(prompt, mode); * -------------------------------------------- * This function prompts the user for a file name using the * prompt string supplied by the user and then attempts to * open that file with the specified mode.  If the file is * opened successfully, OpenUserFile returns the appropriate * file pointer.  If the open operation fails, the user is * informed of the failure and given an opportunity to enter * another file name. */static FILE *OpenUserFile(string prompt, string mode){    string filename;    FILE *result;    while (TRUE) {        printf("%s", prompt);        filename = GetLine();        result = fopen(filename, mode);        if (result != NULL) break;        printf("Can't open the file \"%s\"\n", filename);    }    return (result);}/* Section 2 -- Functions to process the course *//* * Function: ProcessCourse * Usage: ProcessCourse(course); * ----------------------------- * This function processes the course supplied by the caller. * The basic operation consists of a loop that * *    (a) prints out the current question *    (b) reads in an answer *    (c) looks up the answer in the database *    (d) goes to a new question on the basis of that answer * * In this implementation, the variable qnum holds the * index of the question and the variable q holds the * actual question data structure.  The course always begins * with question #1, after which the order is determined by * the answers. */static void ProcessCourse(courseDB course){    questionT q;    int qnum;    string ans;    int index;    printf("%s\n", course->title);    qnum = 1;    while (qnum != 0) {        q = course->questions[qnum];        AskQuestion(q);        ans = ConvertToUpperCase(GetLine());        index = FindAnswer(ans, q);        if (index == -1) {            printf("I don't understand that.\n");        } else {            qnum = q->answers[index].nextq;        }    }}/* * Function: AskQuestion * Usage: AskQuestion(q); * ---------------------- * This function asks the question indicated by the questionT * specified by q.  Asking the question consists of displaying * each of the lines that comprise the question text. */static void AskQuestion(questionT q){    int i;    for (i = 0; q->qtext[i] != NULL; i++) {        printf("%s\n", q->qtext[i]);    }}/* * Function: FindAnswer * Usage: FindAnswer(ans, q) * ------------------------- * This function looks up the string ans in the list of answers * for question q.  If the answer is found, its index in the * answer list is returned.  If not, the function returns -1. * The function uses a simple linear search algorithm to look * through the array. */static int FindAnswer(string ans, questionT q){    int i;    for (i = 0; i < q->nAnswers; i++) {        if (StringEqual(ans, q->answers[i].ans)) return (i);    }    return (-1);}