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Answers in Software Development | By Some Guy

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Tags: C++, Errors, Programming, Signed Integer, Unsigned Integer

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I work a lot in Java and Python, but I do not have a wealth of experience programming in C++. I have been forced to recently, and have been running up against this warning: "Comparison between signed and unsigned integer expressions." What does this mean, and how can I fix this?

Download more RAM. 🐏 ⨉ 0Posted by Some Guy 2 years ago 🕓 Posted at 16 December, 2018 09:27 AM PST

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Profile Photo - August R. GarciaAugust R. GarciaLARPing as a Sysadmi...Portland, ORSite Owner

This warning is raised because signed and unsigned integers cover different ranges. Unsigned integers must be positive numbers (or zero), whereas signed integers can be negative, positive, or zero. This can cause inaccurate comparisons to occur due to the way that the compiler handles this situation.

The C++ compiler will cast the signed integer as an unsigned integer before comparing the two values. Because of this, this warning is a warning rather than an error. This means your code will technically still work in many cases, however, it also means that in if your signed integer is negative, an integer overflow may occur, causing the signed integer to be cast into a (large) positive integer.

The best solution depends on your specific problem. This page by James W. Walker goes into a few potential solutions:

Download more RAM. 🐏 ⨉ 0Posted by August R. Garcia 2 years ago 🕓 Posted at 19 December, 2018 09:28 AM PST

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Profile Photo - DefaultHellothere404

C++ compiler gives warnings about something like a comparison between signed and unsigned variables. Compilers give this warning because the ranges of the signed and unsigned ints are different, so if we compare them it can give unwanted results.
The last bit in signed types represents the sign of the number because of the difference of evaluation between signed and unsigned in their last bit. Actually it makes a difference if we compare -1 or +9.

To avoid this issue use the exact type you are comparing against, and it is a good idea to declare variables as unsigned or size_t if you are planning to compare them to sizes. If you’re wondering about how to declare the exact type so see this carefully → use std::string::size_type when comparing with an std::string’s length.
If you have to make the comparison in between two int of different ranges then you should definitely explicitly convert one of the values to s type compatible with the other but make sure that the conversion is valid.

For example check this example, 

https://kodlogs.com/blog/113/comparison-between-signed-and-unsigned-integer-expressions

Hope this will help.

Download more RAM. 🐏 ⨉ 0Posted by Hellothere404 10 months ago

Edit History

• [2020-11-23 12:44 PST] Hellothere404 (10 months ago)
🕓 Posted at 23 November, 2020 12:44 PM PST

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