Test cases for numeric input

Question

What are some common (or worthwhile) tests, test questions, weaknesses, or misunderstandings dealing with numeric inputs?

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For example, here are a couple sample ideas:

• I commonly see users enter text into number fields (eg, ">4" or "4 days", etc).
• Fields left blank (null)
• Very long numeric strings
• Multiple decimals and commas (eg, "4..4" and "4,,434.4.4")
• Boundary Value Analysis:
  • Lower Boundary
  • Lower Boundary - 1 (for decimal/float, use smaller amounts)
  • Upper Boundary
  • Upper Boundary + 1
  • Far below the lower boundary (eg, beyond the hardware boundary value)
  • Far above the upper boundary
  • middle of the range
• 0
• 0.0
• White space, nothing else " "
• String input & other incorrect data types.
• Number with text in front or back, eg "$5.00", "4 lbs", "about 60", "50+"
• Negative numbers
• + sign with positive numbers, "+4"
• Both plus and minus sign, eg "+-4" and "-4e+30"
• Exponents of 10, both uppercase and lowercase, positive and negative eg "4e10", "-5E-10", "+6e+60", etc
• Too many "e" characters, eg "4e4e4" "4EE4"
• Impossibly large/small exponents or inappropriate ones
• Decimal values that cannot be represented in a computer
  • eg, .3 + .6 == 1.0? This bug affects most hardware, so outputs that compare decimal values should allow for a degree of error.
• Integer/hardware overflow. Eg, for 32-bit integers, what happens when adding 4 billion to 4 billion?
• wrong use of decimal sign and thousands seperator ("," vs. ".") (MikeD)
• internationalisation i18n issues: In english aplications you write "12,345.67" meaning "12345.67" in german you write "12345,67" – (k3b)
• leading 0's don't make number octal (common javascript bug)