CS50 Week 1 Shorts

Question 1

Who were boolean values named after?

Answer 1

George Boole

Question 2

What are the two possible conditions of a boolean value?

Answer 2

True and False

Question 3

What are the boolean operators in C?

Answer 3

And &&
Or ||
Not !

Question 4

what are the possible permutations of an AND expression?

Answer 4

TRUE and TRUE = TRUE
TRUE and FALSE = FALSE
FALSE and TRUE = FALSE
FALSE and FALSE = FALSE

Question 5

What are the possible permutations of an OR expression?

Answer 5

TRUE and TRUE = TRUE
TRUE and FALSE = TRUE
FALSE and TRUE = TRUE
FALSE and FALSE = FALSE

Question 6

What doe the NOT operator do?

Answer 6

It takes a boolean operator and returns the opposite of it.

Question 7

What are the numerical representations of TRUE and FALSE in C?

Answer 7

0 = FALSE

Everything else = TRUE

Question 8

What are the four major steps of the clang compiler?

Answer 8

1) Pre-processing, done by the pre-processor.
2) Compiling, done by the compiler.
3) Assembly, done by the assembler.
3) Linking, done by the linker.

Question 9

What does the pre-processor do?

Answer 9

It recognizes pre-processor directives like #include and #define.

Libraries that are #included are appended to the top of the source code.

Constants that are #defined are replaced with their respective values.

Question 10

What is the clang command to only run the pre-processor?

Answer 10

-E

Question 11

What is the clang command to send your output to a new file?

Answer 11

> filename.c

Question 12

What is done during the compiling portion of the compilation process?

Answer 12

The source code is converted to assembly code.

This is called compiling into assembly code.

Question 13

What is the clang command to only run through the compilation step?

Answer 13

-S

Question 14

What happens during the assembly portion of compilation?

Answer 14

The assembly code is converted into “object code,” or “machine code”.

Question 15

What is machine code?

Answer 15

The actual 1’s and 0’s that the computer can read.

Question 16

Why is the same source code compiled into different assembly code on different computers?

Answer 16

The assembly code is processor specific.

Question 17

What is the clang command to only go through the assembly phase of compilation?

Answer 17

-c

Question 18

What happens during the linking phase of the compilation process?

Answer 18

The linker combines together object code from different files into one file.

Question 19

Why is it a good idea to run clang on every file?

Answer 19

Because linking can be very system specific.

Question 20

What must be contained in at least one of the object files?

Answer 20

a main() function.

Question 21

What is the clang command to link a file into the finished file?

Answer 21

• l + the file name.

- lname

Question 22

Where do -l arguments go?

Answer 22

The end of the clang command.

Question 23

Where do -l arguments go?

Answer 23

The end of the clang command.

Question 24

What are three other terms for functions?

Answer 24

procedures, sub-routines, and sub-programs

Question 25

What is the term for the organizational benefit of functions?

Answer 25

encapsulation

Question 26

What are the inputs to a function called?

Answer 26

Arguments, or parameters.

Question 27

Must a function take an argument, or return something?

Answer 27

No to both

Question 28

What is the term for the declaration of a function?

Answer 28

The prototype

Question 29

What is the return type for a function that returns nothing?

Answer 29

void

Question 30

What is a side effect?

Answer 30

When a function has an effect other than its return value.

Question 31

What is the return type of main()?

Answer 31

int

Question 32

What are the arguments allowed for main()?

Answer 32

int argc | char* argv[]

Question 33

What does argc contain?

Answer 33

The number of command line arguments passed into the program.

Question 34

What does char* argv[] contain?

Answer 34

The string representations of the command line arguments passed.

Question 35

In general, what is a library?

Answer 35

a collection of related, prewritten code.

Question 36

What kind of files does a library consist of?

Answer 36

A library is a binary file that has been produced by linking together a collection of object files using a linker.

Question 37

What two kinds of files do libraries typically consist of?

Answer 37

header files and implementation files.

Question 38

What is the file extension for a header file?

Answer 38

.h

Question 39

What does a header file describe?

Answer 39

``` The resources available in the library. This can include: functions variables structs type definitions etc. ```

Question 40

What is a common term for the resources described in a header file?

Answer 40

The interface.

Question 41

Why are there no function definitions in the header file?

Answer 41

Information hiding, or encapsulation. It protects the user from changes in implementation.

Question 42

What is the file extension for the implementation file?

Answer 42

.c

Question 43

What does the binary library file consist of?

Answer 43

The header and implementation files, after they have been compiled and linked together.

Question 44

What will the library writer ship?

Answer 44

The header file and the binary file.

Question 45

What two things are needed to use a library?

Answer 45

#include the header file above main() Link the binary file during compilation.

Question 46

What are the two syntaxes used to include a header file?

Answer 46

#include if the header file is in the default include library, which is typically usr/include. #include "header.h" if the header file is in the same directory as the program it is being appended to.

Question 47

What is make?

Answer 47

A program that organizes invocations of commands to the compiler, ensuring that things are compiled in the proper order and in the proper way.

Question 48

What is the make command to compile a file?

Answer 48

make file

Question 49

What is the default output for clang?

Answer 49

a.out

Question 50

At the most basic level, what is the command to run clang on a file?

Answer 50

clang file.c

Question 51

What is the clang command to control what the name of the output is?

Answer 51

-o clang file.c -o file would result in file.c being compiled into an executable file called "file"

Question 52

What clang flag controls the warnings that clang produces?

Answer 52

-w

Question 53

How do you turn on all warnings in clang?

Answer 53

-wall

Question 54

How do you stop the compiler from creating an executable if it hits an error?

Answer 54

-werror

Question 55

What clang flag allows gdb to be run?

Answer 55

-gdb

Question 56

What clang flag links libraries into your code?

Answer 56

-l

Question 57

What is typecasting

Answer 57

A way of changing how the computer interprets data, either implicitly or explicitly.

Question 58

What can happen to precision during typecasting?

Answer 58

Precision can be lost, but never gained.

Question 59

What part of a float is maintained if you cast it into an int?

Answer 59

The part before the decimal, all else is truncated (not rounded).

Question 60

How is explicit typecasting done?

Answer 60

(type) variable | example: (int)x

Question 61

What is implicit typecasting?

Answer 61

When the computer automatically casts into another type. An example is adding an int and a float. The int is automatically cast into a float so that the operation can be performed.

Question 62

Can implicit typecasting happen with the and == operators?

Answer 62

Yes

Question 63

What is the difference between i++ and ++i?

Answer 63

When i++ i used, the value of i is used in the expression then the incrementing happens. With ++i, the incrementing happens first.

Question 64

Which happens first, incrementing or dereferencing?

Answer 64

Incrementing.

Question 65

What must be done before a variable can be used?

Answer 65

It must be declared.

Question 66

When naming variables, how are words separated?

Answer 66

With an underscore. this_is_a_name

Question 67

While C does not use this for variable names, what is camel case?

Answer 67

When the first word is lower case, and the first letter of following words is capitalized. thisIsCamelCase

Question 68

What is happening when you assign one variable to another variable? i.e x = y

Answer 68

The value of x is set to the value of y, but it is a copy, not a pointer to the same value as y. Changing y later will not change x.