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Creating Learning Networks for African Teachers

UNESCO PROJECT (Contract No. 408.302.9)

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SPREADSHEETS TUTORIAL

EXAMPLE: AN INTERACTIVE BASE CONVERTER

Rationale
It is often useful to be able to demonstrate the mechanisms employed in performing number base conversions. In particular, it is useful to demonstrate base conversion where complex bases are involved. With bases higher than 10, the letters A, B, C, D, E, and F are used to represent digits from 10 to 15.

Tools
The demonstration employs the Microsoft EXCEL application package. EXCEL has features that can be exploited to execute this activity. The features employed include using the VLOOKUP feature to pick the values associated with input digits. The function POWER(base, positional exponent) is used to consolidate the position values using the algorithm:

Number = ådigitj * base positional value of digit

Methodology
The user is prompted to supply a number to be converted from a given base into base ten. The base of the source number is therefore also input interactively by the user.
The user should enter the number composed of a maximum of four digits one digit per cell in the set of cells in columns EFGH. For each of the digits entered, the application looks up the associated decimal equivalents taking into account that the base could go up to hexadecimal or base sixteen. Accordingly, the lookup table has a mapping for each of the sixteen possible digits 0, 1, ,9, A, ,F.
Table-array

 
Digit
Decimal equivalent
0
0
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
A
10
B
11
C
12
D
13
E
14
F
15

The VLOOKUP function accordingly takes the following shape VLOOKUP(value-to-be-matched, table-array-range, column-of-target-value, k) Where: value-to-be-matches the digit entered by the user and in the formula is represented by the cell address. Table-array-range is the range reference to the lookup table that indicates the decimal equivalent of each digit. Column-of-target-value indicates the column within the table-array where the actual values are stored.


Click here
to experiment with the application interactively.
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