Week 1 - C

Question 1

Briefly define source code and machine code.

Answer 1

• Source code is the version of software as it is originally written by a human in plain text.
• It is a group of instructions a programmer writes using computer programming languages.
• The source code is is later turned into machine code, also called object code, that a computer can understand and execute.
• Machine code is a computer programming language consisting of binary or hexadecimal instructions which a computer can respond to directly.

Question 2

What is a compiler?

Answer 2

1. A compiler is a program that translates computer code written in one programming language into another language.
2. The original code is called the source code, and the resulting code is called the object code or the machine code.
3. The process of transforming source code into object code or machine code is called compilation.
4. A compiler allows a human programmer to write code that can be understood and executed by a specific CPU.

Question 3

What is the difference between a GUI and a CLI.

Answer 3

• The command-line interface (CLI) and graphical user interface (GUI) are two different ways for users to interact with an operating system.
• The key difference between the CLI and GUI is that the interaction with CLI is based on issuing commands.
• In contrast, the interaction with a GUI involves visual elements, such as windows, buttons, etc.
• Both interface types have advantages and disadvantages, but their purpose is the same.

Attached example of a CLI

Question 4

What is the significance of the $ sign in the terminal window?

Answer 4

It means “type commands here”.

Question 5

What is the syntax in C for displaying text in the console and what does each part mean? (the console is the terminal window or te cli window where the program outputs results)

Answer 5

printf("some text\n");

• printf - the command to print text. “f” is for “formatted”. It allows you to print output with some formatting included.
• the () curley braces are for specifying what the parameters will be for the function. In this case the printf function expects some input like text to print.
• " - Every time you write text you need to quote it. like "hello, world"
• \n - Means formatting for a newline. the \ is an “escape” character, which means that the next part of text is not part of the string of words.
• ; - This is the end of the statement.

Question 6

what does #include <stdio.h> do in C?

Answer 6

1. stdio.h is Standard Library that provides input and output capabilities for C programs.
2. In C we call this a “header file”
3. It contains more than 40 functions that are used to perform input and output operations. The acronym stdio stands for Standard Input and Output.
4. With this piece of code you are telling the program to include other code that has already been written into your own program.
5. Among other things it makes the printf function avaialble for use in your code.

Question 7

Why do you need to recompile code?

Answer 7

Whenever you change your source code you need to recreate or update the binary file. This means “recompiling” the code.

Question 8

Define return value.

Answer 8

Its a value you get back from a function that you can use/read. Its the output value of a function.

Question 9

What is the code to ask the user for an input with C?

Answer 9

string answer = get_string("What's your name? ");

Question 10

What is the purpose of the = sign in C?

Answer 10

1. Its the “assignment” symbol.
2. It assignes the value on the right to the left of the sign.

Question 11

What type is used for a variable that is assigned to words?

Answer 11

1. string
2. string is a type for a variable that needs to store a “string” of words.

e.g. string MyName = "cilliers";

Question 12

What is the purpose of assigning a “type” to a variable?

Answer 12

You are informing the computer what “type” of data is going to be assigned to the variable.

Question 13

In C how do you combine a value from a variable into a string?

Answer 13

• the %s value is used as a placeholder.

printf("hello, %s",anwers);

Question 14

What is the command for creating a new file named “hello” in C?

Answer 14

$ code hello.c

Question 15

Exercise - In VS Code:
1. Create a new C file called “helloWorld”
2. Write a program that will print “hello world” to the command line internface.

Answer 15

Question 16

Write the code to do an if else which prints out if X is larger than Y or if its the same.

Answer 16

Question 17

What does = mean in C and what do you do when you want to copare if some values are equal?

Answer 17

The = sign is an assignment character. It assignes the value on the variable on the left.
If you want to compare values you need to write the coparitor == which evaluates if the value on the left is the same as the value on the right.

Question 18

What is the difference in using " or ' in C?

Answer 18

When dealing with strings or multiple lines of characters you need to use " when deliberately dealing with single characters you need to use '. Single characters are “char” types as opposed to “string” types.

It is meant to ensure that the computer knows you are working with a char.

Question 19

How do you write an OR condition in C?

Answer 19

||

e.g. 
if (x = 2 || x =1){
//do something
}

Question 20

What does this code do and how can you simplify it?
~~~
int counter = 5;
counter = counter+1;
~~~

Answer 20

First line initializes a variable of type int named counter and assignes a value of 5.

Second line adds 1 to the counter. Assignment says that the value on the right is assigned to the variable on the left. Meaning counter+1 is equal to 6 and is assigned to counter on the left. Counter is now 6.

To simpify it C allows you to write counter+=1;

Or even, in the case of integers where you just want to increment by 1 you can write counter++;

Question 21

How would you write a “while loop” in C to loop 3 times and print a string? How would you then simplify that?

Answer 21

int counter = 3;
while (counter > 0)
{
    printf("mystring /n");
    counter--;
}

**simplification**

for(int x = 0; x <3; x++)
{
    printf("mystring /n");
}

Question 22

Write a “while loop” that wil continue forever.

Answer 22

while (true)
{
do the code;
}

Question 23

What is the cli command to display files in a folder and what is special about the * files?

Answer 23

ls

Typing ls in CLI wil list all the files in a folder.
Files with the * extension are executable files. a.k.a. programs. when you type ./thefilesname the computer wil execute the program.

Question 24

How do you rename a file in the CLI in Linux?

Answer 24

mv nameoffile newnameoffile

mv means move and allows to rename and move

Question 25

how do you change folders in the command line for Linux?

Answer 25

cd

You need to add the relative math to the folder. Moving up a filder would be
~~~
cd ..
~~~

moving into down into a folder would be

cd ./myfolder

Question 26

What are the common linux CLI commands?

Answer 26

cd - change directory
cp - copy
ls - list files in directory
mkdir - make a new directory (create a folder)
mv - move
rm - remove
rmdir - remove directory/folder

Question 27

Explain what a do while loop does and write an example.

Answer 27

A do while loop wil do somthing first, then check the condition and repeat if the condition is not met.

Question 28

How do you write comments in C?

Answer 28

// some comment that is one line

Question 29

Write a reusable function that asks the user for an input and returns it. Explain what the definition of the function means.

Answer 29

Question 30

Write a function that takes an integer input and prints it, but does not return anything.

Answer 30

Question 31

Why can’t you use functions in the main method that are only declared later in the file?

Answer 31

C expects things to be included and delclared before the main function when compiled. You will need to declare the function signature at the top of the file and then you can use the function later in the file.

Question 32

How many bits do integers represent and what is the max value based on that?

Answer 32

32bits.

32 bits is 4.2billion

Because you also need to be able to represent negative numbers you only have about 2 billion numbers available.

Question 33

What type of value do you need for larger value than an int?

Answer 33

Use a long.
Long uses 64 bits.
64 bits is 9quintillion

Question 34

What type do you need to use if you want to use decimal valuables?

Answer 34

float
Float is 32 bits.
Float allows decinals.

If you need more you can use a double.

Question 35

How would you cast a value from long to float?

Answer 35

float z = (float) x / (float) y

Question 36

With a float, how do you print out only 20 decimal spaces?

Answer 36

Question 37

What is floating-point inprescision?

Answer 37

when you use a type like float its only 32bit so if the value goes beyond the size the computer will start giving incorrect digits after a certain point. You can use a double for more values,

Question 38

How much space does a “char” take?

Answer 38

8 bits

Question 39

Explain what “Long” and “Double” types are.

Answer 39

• Long is a 64bit integer.
• Double is double precision is a 64bit integer with decimal spaces.

Question 40

What are the string format codes for int, long, float, double, char, string.

Answer 40

Question 41

What is the integer data type?

Answer 41

Question 42

What is an unsigned Int?

Answer 42

You can get 0 to 4 billion positive values.

Question 43

What is a char data type?

Answer 43

Ascii maps the positive values to numbers.

Question 44

What is a float data type?

Answer 44

Question 45

What is a double data type?

Answer 45

Question 46

What is the void type?

Answer 46

Question 47

What are the 5 primitive types in C?

Answer 47

These data structures can be used to store only a single value. They are the foundation of data manipulation. The primitive data structures in C (also known as primitive data types) include int, char, float, double, and pointers.

Question 48

What is the bool type?

Answer 48

The C programming language does not have a built-in Boolean data type like some other programming languages such as Java or Python. However, in C, the standard practice is to use integers to represent Boolean values, where 0 represents false and any non-zero value represents true.

Question 49

What is a string type?

Answer 49

The C language does not have a specific “String” data type, the way some other languages such as C++ and Java do. Instead C stores strings of characters as arrays of chars, terminated by a null byte.

Question 50

How do you create variables?

Answer 50