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 Calculate MOD11 control number
Pico

 Joined: 18 Jan 2004 Posts: 240 Location: HostMachine.net
 Posted: 7.7.2009, 21:08
Many banks use MOD 11 algorithm to calculate control number for verification whether the main number is correct or not, mostly to avoid input errors when typing.
Also, many reference numbers on bills or invoices use the same MOD11 algorithm to be safe from user typografic errors.

MOD 11 principle:

- first, you split given number into separate cyphers, for example:
125111
is split into
1 2 5 1 1 1

- then you take each cypher, and multiply it with so called "ponder". First ponder is 2, then 3, 4, 5, 6, etc... You start multiplying from the RIGHT side, and then SUM all results, for example:
1x2 + 1x3 + 1x4 + 5x5 + 2x6 + 1x7 = 53

- then you DIVIDE final result by 11 (it is MOD11, that's why 11), for example:
53 / 11 = 4 (with reminder of 9)

- Finally, you take reminder of latest calculation and substract it from 11 (yes, 11 again), for example:
11 - 9 = 2

And 2 is control number in MOD11 operation.

Ok, let's calculate MOD11 with PHP script:
 Code: function mod11(\$num) {    \$pond = 2;    \$sum = 0;    \$numRev = ereg_replace("[^0-9]", "", strrev(\$num));    for(\$i=0;\$i

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