Defining a function #include int square(int number); // function prototype int main(void) { int x = 2; printf("x is %d\n", x); x = square(x); printf("x is %d\n", x); return 0; } int square(int number) { int output = number * number; return output; }
Your turn Write a function that takes 2 parameters, number and exponent, and returns number raised to the power of exponent. #include int power(int number, int exponent); // function prototype int main(void) { int x = 2; int third = power(x, 3); printf("%d raised to the power of %d is %d\n", x, 3, third); int fifth = power(x, 5); printf("%d raised to the power of %d is %d\n", x, 5, fifth); return 0; } int power(int number, int exponent) { // ... }
Command-line arguments int main(void) { return 0; } int main(int argc, char *argv[]) { return 0; } argc is an integer representing the number of arguments passed to the command line argv[] is an array of strings that contains the arguments passed to the command line
Command-line arguments fjw22@ide50:~/workspace $ ./copy infile outfile 1. What is argc? 2. What is argv[0]? 3. What is argv[1]? 4. What is argv[2]? 5. What is argv[3]? 6. What is argv[4]?
Modulo • Modulo provides the remainder when dividing two numbers • In Caesar, what happens if we are given a really large number as our key? • In Vigenère, what happens if we reach the end of our target word? 26 % 10 // 6 13 % 12 // 1 8 % 8 // 0 2 % 15 // 1
Grading • Scope: to what extent does your code implement the features required by our specification? • Correctness: to what extent is your code consistent with our specifications and free of bugs? • Design: to what extent is your code written well (i.e., clearly, efficiently, elegantly, and/or logically)? • Style: to what extent is your code readable (i.e., commented and indented with variables aptly named)?
Comment your code! /** * caesar.c * Frank Wu * September 23, 2015 * * Encrypts user-supplied plaintext using a Caesar cipher. */ /** * Returns number^exponent (and ignores all negative exponents) */ int power(int number, int exponent) { // ... }
An example // ??? if (isupper(message[i])) { message[i] = ((message[i] - 'A' + key) % NUM_LETTERS) + 'A'; } else if (islower(message[i])) { message[i] = ((message[i] - 'a' + key) % NUM_LETTERS) + 'a'; } In a few months, will you still remember what this block of code does?
Debugging with gdb fjw22@ide50:~/workspace $ check50 2015.fall.pset2.caesar caesar.c :) caesar.c exists :) caesar.c compiles :) encrypts "a" as "b" using 1 as key :) encrypts "barfoo" as "yxocll" using 23 as key :( encrypts "BARFOO" as "EDUIRR" using 3 as key \ expected output, but not "EAUIRR\n" :) encrypts "BaRFoo" as "FeVJss" using 4 as key :) encrypts "barfoo" as "onesbb" using 65 as key :) encrypts "world, say hello!" as "iadxp, emk tqxxa!" using 12 as key :) handles lack of argv[1]
Problem set 3 • We’ll be using distribution code! • In find.c, your goal is to fill in the sort() and search() functions • In the game of fifteen, your goal is to write a few core functions to finish the game • Hacker edition: create a solver for the game of fifteen
Files in C // Open file "input.txt" in read only mode FILE *in = fopen("input.txt", "r"); // Make sure fopen() doesn't return NULL! if (in == NULL) { return 1; } else { // Close the file at the end to avoid memory leaks fclose(in); }
Pointer exercise int x = 2, y = 8, z = 12; int *ptr_x = &x; int *ptr_y = &y; int *ptr_z = &z; z = x * y; x *= y; y = *ptr_x; *ptr_x = x * y; ptr_x = ptr_y; x = (*ptr_y) * (*ptr_z);
Quiz 0 http://cdn.cs50.net/2015/fall/quizzes/0/yale.html • CPSC 100 01 (lectures on Mondays and Wednesdays) • last name A - N: go at 1:00pm on Wed 10/14 to the Yale Law School Auditorium • last name O – Z: go at 1:00pm on Wed 10/14 to Davies Auditorium in the Becton Center • CPSC 100 02 (lectures on Tuesdays and Thursdays) go at 2:30pm on Thu 10/15 to SSS 114
Practice Question 2 • True or false: • gdb is a debugger • make is a compiler • the float datatype can store infinitely precise decimal numbers • all .c files must have a main function
Practice Question 3 • What happens when I call the following commands: • printf(“%p” , wp); • printf(“%d” , *wp); int w = 2, x = 3, y = 4, z = 5; int *wp = &w; int *xp = &x; int *yp = &y; int *zp = &z;
Practice Question 4 This code was meant to simulate counting from 1 to 10, pausing one second between numbers, it instead appears to do nothing for ten seconds, after which it finally prints everything all at once before quitting. Why? for (int i = 1; i <= 10; i++) { printf("%d, ah ah ah... ", i); sleep(1); }
Stack Suppose that a stack for integers is defined per the below, wherein numbers is an array for the stack’s integers, CAPACITY (a constant) is the stack’s capacity (i.e., maximal size), and size is the stack’s current size. typedef struct { int numbers[CAPACITY]; int size; } stack; Complete the implementation of push in such a way that it pushes n onto a stack, s, if s isn’t already full. Assume that s has been declared globally. Consider s full only if its size equals CAPACITY. No need to return a value, even if s is full. Your implementation should operate in constant time. void push(int n) { }
Queue Suppose that a queue for integers is defined per the below, wherein numbers is an array for the queue’s integers, CAPACITY (a constant) is the queue’s capacity (i.e., maximal size), and size is the queue’s current size, and front is the index of the integer at the front of the queue. typedef struct { int front; int numbers[CAPACITY]; int size; } queue; Complete the implementation of enqueue in such a way that it inserts n into a queue, q, if q isn’t already full. Assume that q has been declared globally. Consider q full only if its size equals CAPACITY. No need to return a value, even if q is full. Your implementation should operate in constant time. void enqueue(int n) { }
chmod chmod changes the access permissions of file system objects fjw22@ide50:~/workspace $ ls -l total 4 drwx------ 2 ubuntu ubuntu 4096 Oct 26 05:14 directory/ fjw22@ide50:~/workspace $ chmod 711 directory fjw22@ide50:~/workspace $ ls -l total 4 drwx--x--x 2 ubuntu ubuntu 4096 Oct 26 05:14 directory/
ls -l fjw22@ide50:~/workspace $ ls -l total 4 drwx--x--x 2 ubuntu ubuntu 4096 Oct 26 05:14 directory/ permissions owner name owner group file size (bytes) number of links last modified time name
Your turn Create a program that takes in command-line arguments and prints out the first letter of each one on a new line. Hint: use foreach! fjw22@ide50:~/workspace $ php first.php test arg f t a
SQL INSERT INTO table VALUES values # insert into table the row of values INSERT INTO table (col1, col2) VALUES (val1, val2) # insert into table under columns col1 & col2, val1 & val2 INSERT INTO Insert specific values into a database table Example: INSERT INTO `users` (username, hash) VALUES('andi', '$2y $10$c.e4DK7pVyLT.stmHxgAleWq4yViMmkwKz3x8XCo4b/u3r8g5OTnS')
SQL UPDATE table SET col1 = val1, col2 = val2, ... # update table, changing values in particular columns UPDATE table SET col1 = val1 WHERE identifier = "name" # update table, changing col1 to val1 where "identifier" equals "name" UPDATE Update data in a database table Example: UPDATE `users` (username, hash) SET name = 'andy' WHERE name = 'andi'
SQL SELECT col FROM table WHERE col = "identifier" # select the "identifier" column from table to compare/view SELECT * FROM table # select all columns from a table SELECT Select data values from a database table Example: SELECT * FROM `users`
SQL DELETE FROM table WHERE col = "identifier" # delete a row from table DELETE Delete data from a database table Example: DELETE FROM `users` WHERE name = "andy"
Javascript // a simple variable var problems = 99; // an array var mic_checks = [1, 2, 3]; // a string var str = "Testing, testing"; // an object var obj = {receptions: 9, yards: 105, average: 11.7};
Your turn Write a function that takes in an array of words and returns a new array with the first letter of every word capitalized. var cap = capitalize(["joe", "mike", "steve", "kevin"]) cap should now be ["Joe", "Mike", "Steve", "Kevin"] http://jsbin.com/?js,console
Your turn As Professor Malan demonstrated during class, we can AJAX-ify fetching a stock price for pset7. Without referencing the code he showed in class, write a function quote() that will call the appropriate endpoint and then adds the fetched price to the DOM in a span with id ‘price’. You can assume that any required HTML has already been setup.
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