I have a file with the following content:
001
Now if I start a macro (qq), yank this line (Y), paste it (p), increase the number by four (4Ctrlaa), end the macro (q), and execute this macro nine times (9@q), then I end up with following:
001
005
011
015
021
025
031
035
041
045
051
How does this work? I mean why is the third number six (001 + 005) digits larger than second number? Or fifth number six digits larger than fourth number, etc.?
If the number starts with a 0 it's interpreted as an octal number (base-8, instead of base-10). Vim also recognises hexadecimal numbers (base-16) if it starts with 0x and binary numbers (base-2) if it starts with 0b.
You can use the 'nrformats' setting to control which numbers Vim recognises; IMHO a value of bin,hex makes the most sense, as it's not easy to confuse a hex or binary in those formats with a regular base-10 number.
Also see the paragraphs below :help v_g_CTRL-X (no direct help tag).
