C
How many bits are used for integers?
32 bits (4 bytes)
What is the positive and negative ranges for negative and positive integers, respectively?
negative: 2^31
positive: 2^31-1 (-1 because to exclude option 0)
What is an unsigned integer?
a qualifier applied to certain types (int or other data types) that double the positive range of variables of that type at the cost of disallowing negative values
How many bits does char take up?
8 bits (1 byte) with negative range -128 and positive range 127
What American standard ensures the assignment of specific sequence of bits?
the American Standard Code for Information Interchange (ASCII)
What letter maps to the number 65 according to the ASCII standard?
letter A
what number according to the ASCII standard corresponds to the number 0?
48
What are floating-point values?
- also known as real numbers
- contain up to 4 bytes of memory (32 bits)
- limited to how precise we can be
What is the difference between the data types of floating-point values and doubles?
Doubles have DOUBLE the amount of PRECISION:
floating point is 4 bytes (32 bits) and doubles are 8 bytes (64 bits)
Describe the "void" type.
- is a type (not a data type)
- means that functions with void return type don't return a value
- parameter list of a function can be void meaning it doesnt take any parameters
- essentially a placeholder for "nothing"
What are the three terminal commands in cs50.dev used to:
- create a file
- convert it into binary/computer language
- program execution
code filename.c
make filename
filename./
Are boolean data type available in C?
no, booleans are not one of the 5 main data types however by using a library with this data type, booleans can be used
What are the 5 (data) types in C?
integer char, float, doubles, and void
What is a string?
a long series of characters. To use string data types, include the cs50.h header file
What is a string?
a long series of characters. To use string data types, include the cs50.h header file
what is typedefs?
alloes you to create your own data types
what is structs?
a structure : allow you to group an integer and string into one unit (and other types)
to execute a variable, you need...
a data type and variable name
Is this valid?
int height, width;
yes using a common to assign the same data type for several variables is valid
declaration, assignment, or initialization?
int number;
number = 7;
int number = 7;
declaration
assignment
initialization
True or False?
In C, every nonzero value is equivalent to true, and zero is false (boolean)
True
2 main types of boolean expressions?
logical operators - logical AND (&&), logical OR (||) operators
relational operators - tests for equality or inequality, (x > y), (x != y), (x == y)
How are logical NOT (!) operators used?
x !x
true false
false true
logical NOT (!) inverts the value if the operand
What does the function switch() do?
switch(x) {
case 1:
expression;
break;
case 2:
expression;
break;
default:
expression;
}
conditional statement that allows for enumeration of discrete cases instead of using boolean expressions
important to break between each case to not "fall through" each case unless desired
How to use the ternary operator (?:)
int x = (expression) ? 5 : 6;
^ checks expression. if true, assign 5 to variable x and if false assign value 6
in other words, it means...
int x;
if (expression)
{
x = 5;
}
else
{
x = 6;
}
How to use for loops in C?
for (start; expression; increment) {
}
example:
for (int i=0; i<10; i++)
{
}
What is a GUI?
Many modern Linux distributions have graphical user interfaces (GUI) allow easy mouse-based navigation
UNIX-based operating system:
works with apple and Linux (differs from command prompt in microsoft PCs)
What does ls do in the terminal window?
Typing "ls" in the command window lists the files in your workspace
what would typing "cd pset1" do?
Typing this would navigate you to your pset1 folder by using the cd (change directory) command. Typing ls after this, you would see other names if lists in your newly changed directory
ctrl + l OR clear
clears terminal window
How to find where you are in reference to a file?
type "pwd" (present working directory)
what happens if you just type "cd" in the command window?
you will return to your home window tilda
How to make a new directory?
mkdir <directory>
(will make a new subdirectory located in the current directory)
How do you copy files uding the terminak window?
cp <source> <destination>
duplicates the file you specify as <source> which it will save in <destination>
to copy DIRECTORIES, its similar:
cp -r <source> <destination>
where "r" stabds for recursive (tells cp to dive down into the directory and copy everything inside it)
How to remove a file using the command window?
rm <filename>
*note: there is NO recycle bin so confirm your removal kf the file using "y" and "n" keyboard inputs
to avoid *, can force the removal:
rm -f <filename>
to delete a directory:
rm -r <directory>
How to move files using the terminal window?
mv <source> <destination>
allows user to move the file from the location of <source> to the <destination>
Other commands to use in the Linux command line system:
chmod
rmdir
sudo
ln
man
clear
touch
diff
telnet
What is a better way of representing the following in the terminal window?
clang -o hello hello.c
./hello
make ./hello
True or False: If you get an error in your terminal window indicating a oroblrm with one if your functions that is from a library, you can solve the issue by typing the following in the terminal window:
clang -o hello hello.c -lcs50
./hello
note: l in -lcs50 stands for library
True
What is a prototype?
the declaration of a self-defined function in the firnat:
void <filename>(parameter)
... main() ...
4 important steps in C from library to functions in your file via the clang (and make) command:
1. preprocessing: converts #include lines to the underlying prototypes in the file
2. compiling: converts C to assembly language
3. assembly: converts assembly code to the binary code with 0's and 1's for the computer to understand
4. linking: combines compiled binary code from your own file, any #included .h files and stdio.h and links these blocks if code together into one final file of the file name of choice
What function can you use to debug your code and check for logical errors?
debug50 ./buggy
*note: you can click the red circle next to a line (indicates the breakpoint). The debug checker does not run the code on the breakpoint line.
*note: icons at the top of the file allow you to step over or jump into the breakpoint
What are debugging tools available to cs50 students?
printf
debug50
rubber duck (talking to an inanimate object about the steps in your code)
cs50.ai
What is the space (number of bits) allocated to the data types?
TYPE BYTES
bool 1
int 4
long 8
float 4
double 8
char 1
string ?
How is the end of a string identified?
the "break" character /0 (in contrast to just 0 which may be confused
True or False?
Each string ends with \0 in memory
True
What us the char representation of 0?
\0
What is a nul?
a nul represents the termination, or end, of a string by a 0 bit value
what does the following do?
int sequence[5];
initializes an array called sequence with five elements ([5] is NOT a position identifier)
what does argc and argv do?
int main(int argc, string argv[ ])
{
}
argc tells you how many inputs follow the initialization statement ./filename in the command window and argv[ ] actually stores those inputs, for example:
./code 1 2 3 -->
code[0] is ./code
code[1] = 1
code[2] = 2
code[3] = 3
how are arrays different from other variables?
arrays are passed by reference, in other words they are not copied like with other variables but rather the actual array is used (hoping it does not gain an unwanted change). Other variables in C are passedby value in function calls.
what is argc? (command-line arguments)
- Name is a convention
- argc means argument count
- This integer-type argument will store the NUMBER of command-line arguments the user typed when the program was executed
What is argv? (command-line argument)
- name is a convention
- argument vector
- an array of strings the user typed at the command-line when the program was executed
- each element of array is separated by a space when typed
- First element argv[0] is the file name
- last element of argv can be found at element argv[argc-1]
what do O, and theta have in common? (linear searches)
O() is a function that represents the minimum number of steps in a linear search
Ω() is a function that represents the maximum number of steps in a search
Θ() is a function that represents the number of steps when O and Ω are equal (Θ is uppercase theta)