{"id":326,"date":"2020-07-06T20:01:08","date_gmt":"2020-07-06T20:01:08","guid":{"rendered":"https:\/\/aaidm.buas.nl\/?page_id=326"},"modified":"2020-07-06T20:09:46","modified_gmt":"2020-07-06T20:09:46","slug":"pr1-preparation-for-week-4-flow-control","status":"publish","type":"page","link":"https:\/\/aaidm.buas.nl\/?page_id=326","title":{"rendered":"PR1 – Preparation for Week 4 – Flow Control"},"content":{"rendered":"\n
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Author:<\/td>Carlos Santos<\/td><\/tr>
Learning Line:<\/td>Programming<\/td><\/tr>
Course:<\/td>PR1: Introduction to Programming<\/td><\/tr>
Week:<\/td>4<\/td><\/tr>
Competencies:<\/td>Students will be able to effectively define and use variables, programming flow control.<\/td><\/tr>
BoKS:<\/td>\u00ad 3bK2, The student understands the principles of data related software like Python, R, Scala and\/or Java and knows how to write (basic) scripts.<\/td><\/tr>
Learning Goals:<\/td>Variables and Data Types
In-code Comments<\/td><\/tr><\/tbody><\/table><\/figure>\n<\/div><\/div>\n\n\n\n

Flow Control – If… Then.. Else…<\/h2>\n\n\n\n

Before we start with if<\/em> statements, we have to understand a bit better how boolean expressions work.<\/p>\n\n\n\n

Boolean Expressions<\/h4>\n\n\n\n

Boolean are a data structure which may only have two values known as True \/ False. They are important for controlling the path of instructions. <\/p>\n\n\n\n

For example, check if a value is higher than 0.<\/p>\n\n\n\n

a = -1\na > 0\nFalse<\/pre><\/div>\n\n\n\n
There are other boolean operators, that allow you to create more complete expressions. For example, if you want to check if a value is between 0 and 1 (inclusive). <\/p>\n\n\n\n
b = 0.4\nb >= 0 and b <= 1\nTrue<\/pre><\/div>\n\n\n\n
The operation and <\/strong><\/em>only returns True<\/em> if both instances are True. <\/p>\n\n\n\n
Now imagine, you want to check the opposite, check is a number is not between 0 and 1 (inclusive). You can’t write:<\/p>\n\n\n\n
c = 2\nc < 0 and c > 1\nFalse<\/pre><\/div>\n\n\n\n
you have one of the other two boolean operators. <\/p>\n\n\n\n
c = 2\nc < 0 or c > 1\nTrue<\/pre><\/div>\n\n\n\n
The operation or<\/strong><\/em> returns True<\/em> if any of instances are True.<\/p>\n\n\n\n
Alternatively you can take the first expression, and negate it<\/p>\n\n\n\n
d = 2\nnot(d >= 0 and d <= 1)\nTrue<\/pre><\/div>\n\n\n\n
The operation not<\/strong><\/em> inverts the value of a boolean. Note that you may have to use parenthesis, to assure the correct order of operations, similar to the multiplication and addition.<\/p>\n\n\n\n
d = 2\nnot d >= 0 and d <= 1\nFalse<\/pre><\/div>\n\n\n\n
If statement<\/h2>\n\n\n\n
Until now all the instructions that you placed, are executed. If statements allow to conditional execute instructions sets.<\/p>\n\n\n\n
n = 10 \nif n > 0:\n  print("Positive result")<\/pre><\/div>\n\n\n\n
It also allows you to branch your code, and chain multiple instructions, even use alternative branches:<\/p>\n\n\n\n
n = 10 \nif n > 0:\n  print("Positive result")\n  print("Yes!")\nelse:\n  print("Negative result")\n  print("Oh, no...")<\/pre><\/div>\n\n\n\n
Note, that by using if statements you are creating a new scope, which follows the same rule set in the functions<\/a> lecture.  Please revise the scope section, if you don’t recall.<\/p>\n\n\n\n
You can obviously combine this to create more complete functions, for example.<\/p>\n\n\n\n
def maximum(a,b):\n  """\n  Function that returns the highest number between a and b.\n  """\n  if a > b:\n    return a\n  else:\n    return b<\/pre><\/div>\n\n\n\n
if…elif…elif…elif…else<\/h2>\n\n\n\n
There are times that, it is relevant to chain multiple conditions,  the elif<\/em> works exactly like you would chain multiple if else if else<\/em> statements<\/p>\n\n\n\n
def filmRating(recommendedMinimumAge: int)\n    result = ""\n  \tif recommendedMinimumAge >= 18:\n    \tresult = "R18"\n  \telif recommendedMinimumAge >= 16:\n    \tresult = "R16"\n  \telif recommendedMinimumAge >= 12:\n    \tresult = "R12"\n  \telif recommendedMinimumAge >= 9:\n    \tresult = "R9"\n  \telif recommendedMinimumAge >= 6:\n    \tresult = "R6"\n    else:\n    \tresult = "AL"\n    return result\n  \nfilmRating(10)\n'R9'<\/pre><\/div>\n\n\n\n
Further explanation<\/h2>\n\n\n\n
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