8 Basics of Programming

Licensed under the Creative Commons Attribution licence (CC-BY),
either version 4.0 or at your option, any later version. See:
https://creativecommons.org/licenses/by/4.0/

Author:Usmar A. Padow (amigojapan), contact: usmpadow@gmail.com

Written in 2017.

8 Basics of Programming

0. Sequentiality
1. Variables
2. Statements
3. Conditionals/blocks
4. Functions/Types
5. Input/output
6. Loops
7. Arrays/lists 

before we start you can use this page to run python code
https://repl.it/languages/python and this one for C
https://repl.it/languages/c

0.	Sequentiality/Following instructions in order the first thing
we need to learn in order to become a programmer is that instructions
always follow a regular order, usually from top to down (and sometimes
from left to right) for example, if I write: 
BrushMyTeeth();
CombMyHair(); 
GoToWork(); 
it will never got o work before I brush my
teeth and comb my hair… A great program to learn instruction order is
lightbot (which does it from left to right and then top to down, but
the idea is still there) what would happen if I wrote?:
BrushMyTeeth(); 
GoToWork(); 
CombMyHair(); 
well, the answer is that I
would first brush my teeth, but I would get to work unkempt, which
would cause trouble, that is why the order of the instructions in a
program is so important… also because "computers are stupid”(recommend
watching https://www.youtube.com/watch?v=EKWGGDXe5MA ) which is
another thing to keep in mind, with the previous script I just wrote,
the computer will not intelligently know i should comb my hair before
going to work.. computers are just not capable of such decision making
at this level of programming.  If you make a large program, and
shuffle its instructions around, the program will surely not do what
it was originally intended to do by the way in C this woudl also work:
BrushMyTeeth();CombMyHair();GoToWork();
because C seperates
instructions by the semicolons

1.Variables a variable is a place in the computer memory where some
kind of value sometimes a string(some letters),sometimes a number are
stored. like the value 5 or the string “hello”.   a variable can have
a simple name like just the letter x or any combination of letters
like last_name or social_security_number.  if we have a variable
called social_security_number we could assign it the value 123458789
as a sample social security number.  variables as their name implied
can vary, which seems to be different to the mathematical view on
variables, in math if you say x=5 then x is always equal to 5,  but in
programming we can say x=3; and then x=5; and the value would first be
set to 3 and then change to 5.  in the case of a string, the value
between the double quotes will be assigned to the variable, for
example if we had last_name we could assign “Albert Einstein” to it
easily as follows: last_name= “Albert Einstein”. this is in python,
but in C you would need to use strcpy(last_name, “Albert Einstein”);
but beware, because in C if last_name does nto have hte size to hold
“Albert Einstein” undefined things can happen, I will go more into
depht of string on the chapter about arrays because strings in C are
nothing but arrays of charactres Some languages have different
requirements for variable names, for example, some languages require
that they begin with $ such as $total

2. Statements this may be the most difficult part to explain of
programming, almost everything you see in a computer program is a
statement, statements are commonly ended with semicolons, but can also
appear as keywords such as while() or the thing that goes inside the
while(), the ocndition is also a statement init of itslef Lets talk
about assignment statements.  for example, lets take the following
program x=3; x=5; x=x+1; what will be the result of such a program…
well, the first statement, x=3; will set x to 3, then the next
statement x=5; will (maybe counterintuitively to those who know math)
set x to 5, then the final statement  x=x+1; we need to break down
into its parts.  we have the x on the left called an “lvalue” which is
the same as the first x=3;, where the x is what stores the value, then
we have x+1, the value of x at this point of the program is 5 because
it comes after x=5; so when we do x+1 it is the same as doing 5+1, and
then finally we assign that to the lvalue, so at the end of the
program, x will contain 6 which is 5+1.  *(insert m-programmer program
that steps on this program step by step) other kinds of statements we
will look at later in the book are things like function calls, return
statements, conditional statements and boolean statements.  I would
like to touch on boolean statements before we go on.  boolean values.
a boolean value is a value that can either contain a true or false
value.  a boolean statement is something that evaluates(is calculated)
to either a true or false value for example x=5>3;  the x is our usual
lvalue which will store the result of the following operation. the
operation is 5>3 , and since 5 is more than 3, this will evaluate to
true. in the C programming language and many other languages any value
that is not 0 is true, and true is usually 1, so 5>3 will become the
value 1 which will make x equal to 1 which means x is true now. if we
did this instead, x=3>5 then the x would end up being 0 in C.  other
languages like Javascript have actual boolean values which are not
necessarily a number at all, they just contain true or false, so the
variables worn contain a 1 or a 0, instead of that they will actually
contain true or false.

3. Conditionals/block of code a conditional statement is a statement
which give usually two different flow controls depending on wether the
statement it is evaluation is true or false, for example: x=5>3; if(x)
{
	//this block of code which will run
} 
when explaining conditionals I am forced to explain block of code as
well… basically a block of code is an area of code surrounded by curly
braces { } a block of code can contain many statements or just one
statement or even no statements.  but before I go deep into blocks of
code, lets look at the previous example. x became true because of the
first statement in the program, if(x) checks to see if x is true or
false, if it is true it will run the following statement which is
usually a block of code.  If I switch it around to: x=3>5; if(x) {
	//this block of code won't run
}
then the block of code won’t run. because x is false.  we can make
these into shorter programs as follows: if(5>3) {
	//this block of code which will run
} if(3>5) {
	//this block of code won't run
}
the if statement becomes even more useful when we introduce the
“else” statement, for example in the following program: x=5>3; if(x) {
	//this block of code which will run
} else {
	//this block of code won't run
}
now lets get into blocks of code.  what if I wrote the following
program? 
	x=5>3; if(x) {
		//this block of code which will run
		y=10; 
	} else {
		//this block of code won't run
		y=20 
	}
	what would y be at the end of the program execution?
try to solve this yourself.  the answer is: 10 because the block of
code that run made y into 10 then again, lets say the program said
this: 
	x=3>5; if(x) {
		//this block of code won't run
		y=20 y=y+1; 
	} else {
		//this block of code which will run
		y=10; y=y+2;
	} what would y contain at the end of the program?
try to solve this.  the answer is it would contain 12.  why is this?
the reason is that in the first statement of the program x becomes
false then the fi statement tests that to be false, and jumpy to the
else part of the program, where y is set to 10 and then 2 is added to
y *(show a comparison between scratch blocks and a program made in C
like i did to andre) *(show the am I able to vote in Japan flowchart)

4. Procedures/functions now functions need to be broken down into 2
separate parts, the easy part which is a function call and the hard
part which is a function declaration.  in the be inning go this paper
I used three function calls to say what I was telling the computer to
do: BrushMyTeeth(); CombMyHair(); GoToWork(); I think I will use C as
an example of how function declarations should be written, because it
is “explicitly typed” which means you need to write down what kind of
data you get and take from it… in many other languages like Javascript
and Python just don’t use that system at all, but if you are ever in
the situation of needing to learn an explicit typed language, it is
better if you know it beforehand… OK, this is an example of a function
definition: float calculate_tax(float tax_rate, float amount) { return
amount * tax_rate; } this is a function call, let me explain every
part of the function call, the gift “float” is the “return type” or
what kind of information the function will return, the reason why I
used float instead of int (integer), is because floating point
variables will allow me to represent the result of such an operation,
the tax value of some money will usually have a decimal part and the
fractional part of a number, in other words, a number like 3.99 ,
needs to be a float because of the .99 part of the number… and altho
the tax rate here in Japan in currently 0.8% finally amount, again,
since amount can be 3.99 it again needs to be a float number.  by the
way tax_rare and amount are what we call “parameters to the function”
they are the information the function takes in.  then we see a code
block. and the first instruction in the code block is the return
statement…   return takes the following value, evals is (calculates
it) and finally gives that back to the function call.  now lets take a
look at some sample function calls: float candy_value=2.00; float
candy_value_plus_tax; candy_value_plus_tax = calculate_tax(0.8,
candy_value);//this is a function call The first line in C will setup
the value of the candy, in this case 2.00 in a float variable.  The
second line sets up the variable which will eventually hold the value
of the candy after tax.  then comes the function call, first the
parameters are sent tot he function so 8.0 and 2.00 are sent to the
previously defined function… taking their place as tax_rate now being
equal to 8.0 and amount now being equal to 2.00.  then we get return
amount * tax_rate. so int this specific function call, it will be like
this: return 2.00*0.8; first we solve the vale of 2.00*0.8  which is
1.6 then the return statement hands that back to the function call,
and sets candy_value_plus_tax to 1.6

5.Input/output ok, first to explain output you need to understand that
computers used to be connected to something called a teletype, which
was like a typewriter and a printer, and instead of using a screen
they used to print on paper for output…

now, here is the most simple program every programmer starts out with
(in C) #include<stdio.h> int main() { printf("hello world"); return 0;
} or even more simple in python just print “hello world” the C version
needs quite a bit to explain it, first of all, you are including the
stdio.h header file in order to be able to call the printf() function.
then you have the main function definition, main is a special function
in C which is called once per execution of the program. main returns
an integer, which at the end of the program is a 0, which basically
means “the program ended with no errors” now lets look at
printf(“hello world”); which is out output function.  the printf()
function in it’s most simple form just takes a string (which in C is
an array of characters(more on arrays later on)) and prints them on
the teletype or displays them on the screen nowadays.  this program
would literally print hello world  on a piece of paper in the old
days, nowadays it prints it into a “virtual console” or “terminal
program”.  the python version does the same, but with obviously much
more simplicity to it… now lets try putting an integer into our
string: #include<stdio.h> int main() { int a=42; int b=36;
printf("value of a is %i and value of b is %i", a, b); return 0; }
this printf has two placeholders called %i which %i means it is
waiting for an integer value. the first parameter to the printf
statement is “value of a is %i and value of b is
%i” which itself is a string, and contains two placeholders for
%integers. then
the second and third parameters which are a and b which contain the
integers that will replace the two %i’s in the string. then finally
this is computed and printed of the screen.  in python this same
program is quite a bit more simple, it would go as follows: a=42;
b=36; printf "value of a is " + str(a) + " and value of b is " +
str(b) in python the plus sign means “concatenation of string” in this
context, which means python witll take “value of a is “ and connect a
42 to it thenit will connect " and value of b is “ and connect 36 both
the python and C programs will produce the same output, which is:
value of a is 42 and value of b is 36 note that str() is a function
which takes a number and returns a string in python

now lets try some input: #include<stdio.h>

int main() {
	char name[100];
	char lname[100];
	printf("enter your name and last name:");
	scanf("%s %s", &name, &lname); printf("welcome to our program %s %s\n", name, lname);
	return 0; 
}

this program will ask you for your name and last name, and then print
out welcome to our program followed by your name and last name.  first
we reserve 100 characters to hold name and  100 characters to hold
lame, scanf is quite a com-plicated function,  but lets just say that
in this case the two %s means it is expecting two words separated by a
space and stores the first word in name and the second word in lame.
then printf has %s %s which are two placeholders for two separate
strings, one for each variable that is passed, namely name and lname.
finally the string has a \n which in C means it will put a new line at
the end of this print, which means it will scroll down one more line
vdamewood: amigojapan: Variables that are setup inside a function
belong to that function.  Other functions can't see them. But because
we want scanf to send values back when we call it, we use & to give
scanf a special value it can use to write to that value. This value is
called a pointer.  but pointers are one of hte most difficult portions
of C and are beyonf the scope of this tutorial almost the same program
in python: print "enter your name:" name=raw_input() print "enter your
last name:" lname=raw_input() print "welcome to our program " + name +
" " + lname + "\n"

6. Loops 

while loop a while loop is a loop that executed while a condition is
true, and ends when a condition is not true.  an example of a while
loop in C would be:

#include<stdio.h>

int main() { 
	int cont=1; 
	while(cont==1) { 
		printf("continue? 1)Yes 2)No:");
		scanf("%i", &cont); 
	} 
	return 0; 
} 

this program will loop over
and over again until someone hits 2(or any other number other than 1.

notice that the while() expression contains continue==1 instead of
continue=1, this is so that the C programming language can tell the
difference between an equal sign for assignment and an double equal
sign for comparison.  an equal for assignment like continue=1 would
make continue equal to one,  but a double equal sign is for comparison
will take continue which is set to 1 on the line int continue=1; and
compare it to 1, if this is a match, the entire expression continue==1
will be come 1 or true.  and when the contents of the conditional
inside while(conditional) is true, the following block of code will be
run. now lets say the program runs once and the user selects 2, then
it loops back onto while(continue==1) where continue is now 2,
continue==1 is false, so in C it will become 0, and the while loop
will skip to the end of the block, ending execution of the loop and
the program will end. if the user chooses 1, then the contention will
continue to be true, and the program will ask the user for his input
again, until the user no longer chooses 1

the same program in python would be better written like this: cont="1"
while cont=="1": print "continue? 1)Yes 2)No:" cont=raw_input()

note that in python we dont use curly braces, instead of that we use a
tab, or any arbitrary number of spaces to indicate a new block of code
this is designed to reduce the number of lines used when writing a
program.  which brings to mind why I have been writing the programs
withought every line being ("indented"put some spac) even in C, and
the answer is that even if C, eventho it is not a law like in python,
it is still a better idea to indent than not to indent becuase when we
get into blocks inside blocks, it can get very hard to tell which
curly { ends which } so indentation gives us a visual way to recognize
it

do while loop while this kind of loop is not as common as while loops,
it is still useful and can be neatter in certain situations: lets take
these two examples from wikipedia 
do{ 
	do_work();  
}while(condition);

is equivalent to

do_work();
while(condition) {
	do_work();
}

so you can see how we can save ourselves from calling do_work(); twice

for loop for loop is the most prevalent kind of loop in my opinion.  a
for loop had a portions where you initialize a variable, then a
conditional statement, then a portion where you can increment(or do
other operations) with the variable you are using and while while
loops can do anything a for loop can do, it would take up more lines
of code to do the same thing.  so a for loop is a nice shortcut for
writing a loop that repeats a certain ammount of times.

#include<stdio.h>

int main() { int sum = 0; for(int counter = 1; counter < 10;
++counter) { printf("counter is %i and sum is %i\n", counter, sum);
sum += counter; } } norice that sum += counter is just a shortcut form
to type sum = sum + counter the counter is initialized to 1 then the
contition for the loop to continue would be counter < 10 and ++counter
is a shortcut for saying counter=counter+1

we could write the same progrqam using a while loop, as follows:

#include<stdio.h>

int main() {
	int sum = 0;
	int counter = 1;
	while(counter < 10) {
		printf("counter is %i and sum is %i\n", counter, sum);
		sum += counter;
		++counter; 
	} 
}

and in python it would be:

sum = 0
for counter in range(1,10):
	print  "counter is " + str(counter) + " and sum is " + str(sum)
	sum += counter

the output of all of these programs is: counter is 1 and sum is 0
counter is 2 and sum is 1 counter is 3 and sum is 3 counter is 4 and
sum is 6 counter is 5 and sum is 10 counter is 6 and sum is 15 counter
is 7 and sum is 21 counter is 8 and sum is 28 counter is 9 and sum is
36

7. Arrays/lists well, first lets take a look at a simple int array in
C; the easiest way to put information into an array in C is by
"initialising it" I will give hte following example: int myarr[10] =
[9, 8, 7, 6, 5, 4, 3, 2, 1, 0]; this makes an array of 10 integer
elements who's zerowe'th element is can be accessed using myarray[0]
and that will contain the integer 9, it will behave exaactly like an
integer variable once you identify the element you want to access
myarr[1] will contain the integer 8 arr[2] the integer 7 and do on...
note, initialization can only be done when the array is created not
later.  another very important thing to know in C is that we ALWAYS
COUNT FROM 0, that is why it is myarray[0] and not myarray[1] if I
want to change the value of myarray[0]  to 100, as I said, it behaves
exactly like an integer. you just do myarray[0]=100; from then on, tne
contents of the array woud look pretty much like this [100, 8, 7, 6,
5, 4, 3, 2, 1, 0] *important* in C "strings" are really just arrays of
characters. so giving a simillar example to the last one: char
myarr[10] = "hello"; is the same as saying: char myarr[10] =
['h','e','l','l','o','\0']; let me explain this, same the zeroweth
element is myarray[0] and it contains 'h'  , notice we MUST surrouns
single character simbols in single quotes, doubel quotes woudl make it
a string and that is not what this array can hold on each slot. and
the fifth element is '\0' whcih is a special character that means
"string terminator" or "this string ends here" this is because C is
not smart enough to know where the string ends and it needs help to
find out where it ends even back in char myarr[10] = "hello"; this
charracter is automatically appended to the end of the string, it is
just dont "magically"(so we dont notice it) if we make this following
string char mystr[10] = "hellochar myarr[10] = "hello\0world"; and
then try to print that, you will notice that only hello prints, cause
C thinks the string ends at hello.  another thing that is extremly
important about arrays and strings is that you MUST always make sure
there are enough elements to hold the string you are assigning or
copying to it otherwise you will encounted "undefined behaviour"(means
we don't know exactly what will happen, but it is not good) in python
you just make a  string by doing variablename="string" it is that
simple.