Programming Fundamentals: Control Structures, Data Types, Variables, and Expression Evaluation

Fundamental Control Structures

• Sequencing: A fundamental programming structure where all instructions are performed in order and executed one at a time. The computer executes the code sequentially, line by line, from the top to the bottom of the program.

• Selection: A generic term for a type of programming statement that uses a Boolean condition to determine whether or not to select a specific behavior or execute a particular block of statements.

• Iteration: A block of code that repeats instructions to achieve a goal, moving closer to a desired result or repeating until a specified condition is satisfied.

Data Types

Programming structures allow programs to store and manipulate various types of data:

• Integers / Numbers:

  • Made up of digits from $0$ to $9$.

  • Can represent whole numbers or decimal numbers.

  • Can hold positive or negative values.

  • Written directly without quotation marks (e.g., $6.78$ or $3.5$).

• Strings:

  • A sequence or string of characters, options, or full sentences joined together.

  • Always enclosed in single quotation marks '...' or double quotation marks "...".

• Booleans:

  • A data type that can only hold one of two possible values: true or false.

  • Must be written without quotation marks.

Variables and Memory Concepts

• Conceptual Analogy: Variables act like containers within a program.

• Storage and Retrieval Mechanism:

  • Inside the container, specific information required by the program is stored.

  • To access or manipulate the stored information later in the program, it is called by its assigned variable name.

• Variable Rules:

  • Variables can be named virtually anything permitted by the programming language.

  • Each variable can hold exactly one value at any given time.

• Variable Declaration Examples:

  • Numeric Variables:

  • My Money set to $E3.5$

  • Value set to $6.78$

  • String Variables:

  • Work set to "Hello"

  • Sentence set to "This is fake"

  • Boolean Variables:

  • Flag set to true

Operators and Expression Evaluation

• Standard Operators: Standard programming languages include fundamental arithmetic operators for addition ($+$), subtraction ($-$), multiplication ($\times$), and division ($/$).

• Specialized Operators:

  • Modulus (mod): Returns the remainder of a division operation.

  • Logical Operators: Used to evaluate Boolean conditions (AND, OR, NOT).

• Order of Operations: Mathematical and logical expressions follow standard precedence rules (such as BODMAS/BIDMAS).

• Assignment Execution Logic:

  • In any assignment statement, the expression on the right-hand side is always evaluated first.

  • Once the right side is fully calculated, the resulting value is stored into the variable specified on the left-hand side.

  • Overwrite Behavior: If the variable on the left already contains an existing value, that old value is dumped out (overwritten), and the newly calculated value takes its place.

String Concatenation

• Concatenation Operator: The plus sign ($+$) functions as an operator when applied to strings.

• Operation:

  • When the $+$ operator appears between two strings, or between a string and a number, it smashes them together end-to-end to form a longer string.

• Example:

  • "fizz" $+$ "buzz" evaluates to "fizzbuzz".

Code Tracing and Expression Examples

Below are exact tracing scenarios, variable mutations, and evaluation statements:

• Basic Variable Trace:

  • $x = 10$

  • $Y = x + 5$ (evaluates to $15$)

  • $Z = 50$

  • $I = 1 + 5$ (evaluates to $6$)

  • $I = 1 / 5 / 3$

• Variable Mutation Sequence (MYNUM):

  • Initial state: $MYNUM = 2615$

  • Update statement: $MYNUM = 10 + MYNUM \times 2$

  • Evaluation step: $10 + (2615 \times 2) = 10 + 5230 = 5240$

  • Final assignment: $MYNUM = 51$

• Complex Statements and Symbolic Traces:

  • $A = Z - D$

  • $B = E \times 5$

  • $DEN = 1015$

  • $BE = -27$

  • $Fizz = E11$

  • $buzz = B5$

  • Arithmetic expression: $54 / 2211 - 98822.7$

  • $A = A + O$

  • $x = 120$

  • $A = Z - A + X - A$

  • $K = E \times A \times X$

  • Rational calculations:

  • $2201 / 2017$

  • $10 / 40$

  • String variable reference: $AX$