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Need explanation for reported negative sum
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I wrote a simple program that sums the square of integers m -> n. If sum is declared as double it gives something like 4.16..x10^10 for integers 1 -5000. However, if sum is declared as an int, for the same range it reports -1270505460.
Obviously this has something to do with the 4-bytes allocated for int, but vague intuition != explanation. Can someone give me a good explanation for this phenomenon?
Obviously this has something to do with the 4-bytes allocated for int, but vague intuition != explanation. Can someone give me a good explanation for this phenomenon?
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This is because of the size limitations of data types.
an int is only 4 bytes...and has a range from -2,147,483,648 to 2,147,483,647
A double uses 8 bytes (and some floating point algorithm that is beyond my comprehension at the moment) and has a range from +/-1.7E-308 to +/-1.7E308.
Your number simply went out of the range of an integer.
Interestingly enough...integers will simply loop through thaie cycle...i.e. if the number is larger than 2,147,483,647 it will restart the count at -2,147,483,648...whild doubles that exceed their upper limit will cause an error.
an int is only 4 bytes...and has a range from -2,147,483,648 to 2,147,483,647
A double uses 8 bytes (and some floating point algorithm that is beyond my comprehension at the moment) and has a range from +/-1.7E-308 to +/-1.7E308.
Your number simply went out of the range of an integer.
Interestingly enough...integers will simply loop through thaie cycle...i.e. if the number is larger than 2,147,483,647 it will restart the count at -2,147,483,648...whild doubles that exceed their upper limit will cause an error.
Last edited by FC Jamison; Sep 20th, 2006 at 11:39 am.
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Originally Posted by isaacmacdonald 
If sum is declared as double
You can use long and it's variations.
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Originally Posted by isaacmacdonald
sum is declared as an int, for the same range it reports -1270505460.
The key to eliminating bugs from your code is learning from your mistakes.
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Originally Posted by FC Jamison
This is because of the size limitations of data types.
an int is only 4 bytes...and has a range from -2,147,483,648 to 2,147,483,647
A double uses 8 bytes (and some floating point algorithm that is beyond my comprehension at the moment) and has a range from +/-1.7E-308 to +/-1.7E308.
Your number simply went out of the range of an integer.
Interestingly enough...integers will simply loop through thaie cycle...i.e. if the number is larger than 2,147,483,647 it will restart the count at -2,147,483,648...whild doubles that exceed their upper limit will cause an error.
The key to eliminating bugs from your code is learning from your mistakes.
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True...the data types and sizes shown are typical on Windows systems, and the sizes and ranges may be different on other operating systems...
You can determine the size of an integer using
Still...my explanation is the most plausable...he has simply exceeded to range of an int.
You can determine the size of an integer using
sizeof(int);.Still...my explanation is the most plausable...he has simply exceeded to range of an int.
Last edited by FC Jamison; Sep 20th, 2006 at 12:10 pm.
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Instead of double use long long.
If you want to win, you must not loose (Alan Ford)
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If you are working with C++ and your application really demands high precision and range why not try out some third party libraries like these:
http://www.nongnu.org/hpalib/
http://www.tc.umn.edu/~ringx004/mapm-main.html
http://cliodhna.cop.uop.edu/~hetrick/c-sources.html
Though these libraries require you to study them before you use them, they are worth the effort.
HOpe it helped, bye.
http://www.nongnu.org/hpalib/
http://www.tc.umn.edu/~ringx004/mapm-main.html
http://cliodhna.cop.uop.edu/~hetrick/c-sources.html
Though these libraries require you to study them before you use them, they are worth the effort.
HOpe it helped, bye.
I don't accept change; I don't deserve to live.
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Originally Posted by andor
Instead of double use long long.
The key to eliminating bugs from your code is learning from your mistakes.
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I think we lost track of the question...
He wanted to know WHY this happened using an int...not alternatives to using an int.
He wanted to know WHY this happened using an int...not alternatives to using an int.
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Straight from the textbook...
When a variable is assigned a number that is too large for its data type, it overflows. Likewise, assigning a value that is too small for a variable causes it to underflow.
Typically, when an integer overflows, its contents wrap around to that data type's lowest possible value...
When a variable is assigned a number that is too large for its data type, it overflows. Likewise, assigning a value that is too small for a variable causes it to underflow.
Typically, when an integer overflows, its contents wrap around to that data type's lowest possible value...
Last edited by FC Jamison; Sep 20th, 2006 at 1:00 pm.
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