Basic Notes

Excel Sheet

Excel organizes data into a grid structure consisting of columns and rows. Each cell is identified by a unique address derived from the column name and row number.

1. Column Naming

Columns in Excel are identified using letters:

• Columns are labeled from A to Z initially.

• After Z, the column names continue with two-letter combinations:

  • AA, AB, AC, ..., AZ, BA, BB, ..., BZ, CA, ..., and so on.

• This continues up to XFD, which is the last column in modern Excel versions (totaling 16,384 columns).

Examples:

• First column: A

• 26th column: Z

• 27th column: AA

• 702nd column: ZZ

• 703rd column: AAA

• Last column: XFD

2. Row Naming

Rows in Excel are identified using numbers:

• Rows are labeled starting from 1 and increment by 1 for each row.

• Modern Excel versions support up to 1,048,576 rows.

Examples:

• First row: 1

• 10th row: 10

• 1,048,576th row: 1,048,576

3. Cell Addressing

Each cell is uniquely identified by combining the column letter and the row number. For example:

• The first cell: A1 (Column A, Row 1)

• A cell in the 5th column and 10th row: E10

• A cell in the 703rd column and 1st row: AAA1

ASCII Character

ASCII (American Standard Code for Information Interchange) is a character encoding standard used to represent text in computers, communications equipment, and other devices. It uses numeric codes to map characters and symbols to their binary representations.

1. Key Features of ASCII

1. Standard ASCII:

   • Represents 128 characters (0 to 127).

   • Includes:

     • Control characters (0 to 31 and 127) for non-printable instructions like line breaks.

     • Printable characters (32 to 126) for symbols, digits, uppercase and lowercase letters.

2. Extended ASCII:

   • Represents 256 characters (0 to 255) by extending the 7-bit ASCII with an 8th bit.

   • Adds additional symbols, graphical characters, and characters for non-English languages.

2. ASCII Character Groups

Control Characters (0–31, 127):

Non-printable commands for controlling devices.

• Examples:

  • 0: Null (\0)

  • 9: Horizontal Tab (\t)

  • 10: Line Feed (\n)

  • 13: Carriage Return (\r)

  • 27: Escape (ESC)

Printable Characters (32–126):

Human-readable symbols.

• 32–47: Special symbols (e.g., space, !, ", #, $, %).

• 48–57: Digits (0–9).

• 58–64: More symbols (e.g., :, ;, <, =, >).

• 65–90: Uppercase letters (A–Z).

• 91–96: Special symbols (e.g., [, \, ], ^, _).

• 97–122: Lowercase letters (a–z).

• 123–126: Special symbols (e.g., {, |, }, ~).

Extended ASCII (128–255):

Used in systems that support 8-bit encoding. Includes:

• Accented characters (e.g., é, ñ).

• Box-drawing symbols.

• Mathematical symbols.

Power of 2

Power of 2	Exact Value	Approximate Value	Equivalent in Storage (Bytes → KB, MB, GB, etc.)
2⁰	1	1	1 Byte
2¹	2	2	2 Bytes
2²	4	4	4 Bytes (e.g., an int in Java)
2³	8	8	8 Bytes (e.g., a long in Java)
2⁴	16	16	16 Bytes
2⁵	32	32	32 Bytes
2⁶	64	64	64 Bytes
2⁷	128	128	128 Bytes
2⁸	256	256	256 Bytes (1 KB / 4 pages of text)
2⁹	512	512	512 Bytes
2¹⁰	1,024	~1K	1 KB
2²⁰	1,048,576	~1M (Million)	1 MB
2³⁰	1,073,741,824	~1B (Billion)	1 GB
2⁴⁰	1,099,511,627,776	~1T (Trillion)	1 TB
2⁵⁰	1,125,899,906,842,624	~1P (Quadrillion)	1 PB
2⁶⁰	1,152,921,504,606,846,976	~1E (Exabyte)	1 EB

Java Datatype and Memory Size Table

Data Type	Size (Bytes)	Size (Bits)	Minimum Value	Maximum Value	Default Value
boolean	1 (JVM dependent)	8 (for alignment)	false	true	false
byte	1	8	-128	127	0
short	2	16	-32,768	32,767	0
char	2	16	0 (\u0000)	65,535 (\uFFFF)	\u0000
int	4	32	-2³¹ (-2,147,483,648)	2³¹-1 (2,147,483,647)	0
long	8	64	-2⁶³ (-9,223,372,036,854,775,808)	2⁶³-1 (9,223,372,036,854,775,807)	0L
float	4	32	~ ±3.4 × 10⁻³⁸	~ ±3.4 × 10³⁸	0.0f
double	8	64	~ ±1.7 × 10⁻³⁰⁸	~ ±1.7 × 10³⁰⁸	0.0d