1. ENEE150 Discussion 06
Section 0101
Adam Wang

2. Overview
Strings
Pointer Arrays
Project 2

3. Strings
No such thing as a String in C; represented as char arrays
What’s the difference between a char array and a string?
Strings end in the null terminating character “\0”
Only strings can be used for the string library functions
#include <string.h>
Printf(“%s”, s); E N E E 1 5 \0
“ENEE150” =

4. int strlen (char *s)
Takes in a string and returns the size (NOT including the “\0”)
Uses the pointer and moves through the array until is sees the “\0” character
strlen(“enee150”) -> 7
strlen(“a b c d e”) -> 9

5. char *strcpy (char *s1, char *s2)
Copies s2 into s1 and returns pointer to s1
How is this done? Function moves through both pointers putting each char from s2 into s1; stops when reaches “\0”
strcpy(“enee150”, “math”) -> “math150”
What if s2 bigger than s1?
Only stops when it reaches the end of s2; this might cause an error
What if s2 doesn’t have the “\0”
It’ll just keep copying forever; this will definitely cause an error
Why can’t we just do s2 = s1?
Try writing this function and look up online how it’s actually written

6. int strcmp (char *s1, char *s2)
Returns whether s1 comes before or after s2 (alphabetically)
Positive: s1 comes after s2
Negative: s1 comes before s2
Zero: s1 equals s2
Why can’t we just use if (s1 == s2) ?
Strcmp(“bat”, “cat”) -> negative
Strcmp (“cat”, “cat”) -> 0
Strcmp(“carpet”, car”) -> positive

7. char *strstr (char *s1, char *s2)
Looks for first occurrence of s2 in s1 and returns a pointer to it
Returns null if not found
strstr(“concatenation”, “cat”) -> “catenation”
What do the following lines of code do?
char *s3 = strstr(s1, s2);
if (s3 != null)
s3 = strstr(s3 + 1, s2);

8. Pointer Arrays Array of pointers Int a, b, c;
Int *parr[3] = {&a, &b, &c};
Char a[] = “I”;
Char b[] = “Love”;
Char c[] = “Enee150”;
Char *arr[3] = {a, b, c};
0x000.. I \0
0x008.. L o v e \0
0x00C… E n e e 1 5 \0

9. Why not use a 2D array? More wasted memory Bulkier
Char arr2[3][8] = {“I”, “love”, “enee150”};
More reasons later in the course I \0 L O V E N 1 5

10. Project 2 Due Thursday, Oct. 19 First part is due Oct. 12
Recipe Database: Read in recipes (strings), and parse them using the string functions
Three data files: recipes0.data, recipes1.data, recipes2.data
You will ask user which one to read in, then parse it and open the main menu

11. Arrays you should use for this project:
MAX_DATABASE_SIZE is 5MB, so this is 5*1024*1024 characters
Raw_recipes: read entire file into this
Title: read all the recipe titles in
Author: authors of all the recipes
Prep_time_hour: hour of each recipe
Prep_time_min: minutes of each recipe
Categories: Checklist for each category
Ingredients_begin/end: stores the index where the ingredients begin/end
Instructions_begin / end: store the indexes where the recipe instructions begin/end

12. More global vars
All these are optional; depends how you implement your code
all_categories will store each new category as you read it in
num_categories will keep track of how many you’ve read in

13. The ****** isn’t part of it they just signify another recipe
For every recipe:
Put the recipe name into the recipes array
Author into author array
Prep time hour/min into hour/min array
For categories:
Go through existing categories
If current category matches, store the index into categories array
If category doesn’t exist, add it to the all_categories array
Error if more than 8 categories seen
Recipe Header

14. Ingredients
Nothing to parse here; just store the beginning/end index of the ingredients
Alternatively, store the ingredients in a new 2d array

15. Instructions
Again, store the beginning/end index of the instructions in the file array
Or use a new array for instructions
End index of Ingredients/ beginning index of instructions is the “Instructions:” line
End index of instructions is the line containing the *********
Need to print # of recipes seen (basically whenever you see the****)

16. Parsing
Method 1: use getc(inFile) to read in all the chars into the array
Stop when getc(inFile) == EOF  “end of file”
Go to next line: i++ while i != ‘\n’
Skip spaces: i++ while i== ‘ ’
Method 2: use fgets(line, MAX_STRING_LEN, inFile) to read in each line of the recipe file
Stop when fgets == NULL
This also tacks on a \0 to the end of the line array
Then use sscanf(line, “%d,%s,etc”, &var1, &var2, &var3) to parse each line for the information
Would have to create new arrays to store ingredients/instructions

17. Menu After parsing, print out the menu
Keep asking for option while invalid option / not “5”
Just a matter of retrieving data from each array

18. 1. Print Summary For loop for number of recipes
Print out name, author, time, categories as formatted
Only supposed to print a certain # of characters of the entire name/author

19. 2. Print Summary by prep time
Prints recipes that take less than a certain time to make
Ask user for maximum prep time
Keep asking if it’s invalid (hour/min < 0, min > 59)
Then for every recipe, only print the line if time <= what user gives
Recommended to just convert everything to minutes when checking this

20. 3. Print Summary by category
Prints recipe headers in a given category
Ask user for a category
Cycle through all_categories and if not found, keep asking user
If found, use index to check each recipe for matching category and print

21. 4. Print recipe Prints an entire recipe Ask user for ID number
If < 0 or > num_recipes, keep asking for validinput
Print recipe header like in the data file
Print ingredients and instructions using the arrays of indexes

22. Part 1 due next Thursday
List of functions you plan to make and what they do
Some basic ones you definitely should have:
Read_recipes or parse_recipes
Print_summary or print_recipe, etc.
Main_menu function
Like always, lots of opportunities for code reuse
Draw out how to implement the program, then decide what functions will be needed

23. List of functions you may need
Getc
Fgets
Sscanf
Strlen
Strcmp and strncmp
Strcpy and strncpy
Fscanf
Be sure to look these functions up as needed