programming theory 2

7/28/2019 Programming Theory 2

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Operations

Operators vary from language to language but most languages have different operators

that perform similar operations.

Arithmetic Operations

Here are some fundamental arithmetic operators and how they are performed in C++. Assuming a = 6:

Operation Common Operator C++ Example

Addition + >>> a + 2Result: 8

Subtraction - >>> a - 2Result: 4

Multiplication * >>> a * 2Result: 12

Division / >>> a / 2Result: 3

Modulus (Remainder of division)

% >>> a % 2Result: 0

or >>> a % 4Result: 2

Increment ++ >>> a++Result: 7

Decrement -- >>> a--Result: 5

Comparison OperationsComparison/Relational Operators test for some kind of relationship between two values. Assuming a = 6.

Operation Common Operator C++ Example

Equal To == >>> a == 6Result: TRUE

Not Equal To != >>> a != 6Result: FALSE

Bigger Than > >>> a > 10Result: FALSE

Smaller Than < >>> a < 10Result: TRUE

Bigger or Equal To >= >>> a >= 3Result: TRUE

or >>> a >= 8

Result: FALSESmaller or Equal To <= >>> a <= 3

Result: FALSE



Assignment Operations

Assignment operators assign values to variables. The basic assignment operator in most

languages is the equals sign “=”. The below examples are compound assignment

operators which perform an arithmetic operation and then automatically assign the result to

the variable. Assuming a = 6.

C++ Operator C++ Example Same as

+= >>> a += 2a == 8

>>> a = a +2

-= >>> a -= 2a == 4

>>> a = a - 2

*= >>> a *= 2a == 12

>>> a = a * 2

/= >>> a /= 2a == 3

>>> a = a / 2

%= >>> a %= 4a == 2

>>> a = a % 4

Boolean Algebra and Logic Operations

Boolean algebra utilises Boolean data types as discussed in the previous ‘lesson’. Boolean

operations are the same as logic gate operations utilised in electronics/physics, except

derived operators like XOR, NOR, NAND, etc. are not utilised, as there is no need,

considering those are derived from the three basic operators that will be discussed below.

The logic is pseudocodal so the actual operators may vary by language.

Truth Tables

Truth tables are used to show every possible outcome of an operation.

AND operator – Condition 1 AND Condition 2

Condition 1 Condition 2 Result

FALSE FALSE FALSE

FALSE TRUE FALSETRUE FALSE FALSE

TRUE TRUE TRUEResult is TRUE when Condition 1 AND Condition 2 are both TRUE.

OR operator – Condition 1 OR Condition 2

Condition 1 Condition 2 Result

FALSE FALSE FALSE

FALSE TRUE TRUE

TRUE FALSE TRUETRUE TRUE TRUE

Result is TRUE when Condition 1 OR Condition 2 are either TRUE.



OR operator – NOT Condition 1

Condition 1 Result

FALSE TRUE

TRUE FALSEResult is TRUE when Condition 1 is NOT TRUE. Effectively returns the opposite value.

Recap using Python 3.x Examples:>>> a = 10 //Simple assignment

>>> b = 5 //Simple assignment

>>> a == 10 //“Equal to” test

TRUE

>>> b != 5 //“Not equal to” test

FALSE

>>> b > a //“Bigger than” test

FALSE

>>> a == 10 AND b == 7 // Are both “a==10” AND “b==7” TRUE?

FALSE

>>> NOT(a == 10 AND b == 5) //(a == 10 AND b == 5) is TRUE. NOT reverses it.

FALSE

>>> a == 14 OR b == 5 //Is one of “a==14” OR “b==5” TRUE?

TRUE

>>> NOT(a == 14 OR b == 7) //(a == 14 OR b == 7) is FALSE. NOT reverses it.

TRUE

>>> a + b //Addition. Note that the variables are unchanged.15

>>> a * b //Multiplication. Variables are unchanged.

50

>>> a += 2 //a = a + 2. Variable is changed.

>>> a == 12 //a is now equal to 12.

TRUE

>>> a *= 2 //a = a * 2. Variable is changed.

>>> a == 24 //a is now equal to 24.

TRUE>>> a -= 14 //a = a - 14. Variable is changed.

>>> a == 10 //a is now equal to 10, back at its original value.

TRUE

>>> (a - b) == b //a - b is 10 - 5 which is equal to b since b == 5.

TRUE

>>> ((a - b) != b) OR (a > b) //“(a - b) != b” is FALSE, but “a > b” is TRUE.

TRUE

>>> ((a - b) != b) AND (a < b) //“(a - b) != b” is FALSE and “a > b” is FALSE.

FALSE

>>> (a % b) == 0 //Basically checks if b is a factor of a (remainder 0).

TRUE



Sources

http://en.wikipedia.org/wiki/Boolean_algebra

http://www.amazon.com/Cambridge-International-Computing-Coursebook-Examinations/dp/0521186625

http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B










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