Integer types, and integer overflows, in C

C offers you the ability to define a whole variety of integer types:

  short int my_number;

  int my_number;

  long int my_number;

typically occupying 16, 32 and 64 bits of memory (but that is NOT a standard, and you may find different on some systems). And the amount of memory that's declared controls the minimum and maximum numbers that can be held. C, as a language which assumes the programmer knows what (s)he is doing, will not check for overflow for you, and will give results which are plain wrong arithmetically if you exceed the limits.

There's an example [here] from yesterday's C course, where I attempted to fill an array with an exponentially growing series of numbers, and ended up bursting even the capability of a long int. You'll note that (on my machine, in this case), I ended up getting zeros back rather than the largest number the machine can handle - a dramatic failure of my code.

There's a header file - limit.h - which #defines a whole load of constants such as INT_MAX to help you program to check for limits. There's an example of it in use [here] in a training example from our C Programming course.

(written 2012-01-25, updated 2012-01-28)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

C201 - C and C based languages - C Language Fundamentals
  [888] Turning C from source to a running program - (2006-10-06)
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  [2005] Variables and pointers and references - C and C++ - (2009-01-23)
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  [3917] BODMAS - the order a computer evaluates arithmetic expressions - (2012-11-09)
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  [4555] Preprocessor directives in C and C++ - what they mean - (2015-10-27)
  [4566] C - why is slow to write and debug) but fast to run? - (2015-11-01)

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