Скачать или смотреть How to Effectively Count Uppercase, Lowercase, and Digits in a C String Using Pointers

Discover how to correctly implement a character counting function in C for uppercase, lowercase, and digit characters using pointers.
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This video is based on the question https://stackoverflow.com/q/64439014/ asked by the user 'UltraInstinctMessi' ( https://stackoverflow.com/u/14461241/ ) and on the answer https://stackoverflow.com/a/64439057/ provided by the user 'paddy' ( https://stackoverflow.com/u/1553090/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Counting Characters in a C String: A Guide to Using Pointers

Programming in C can sometimes be tricky, especially when it comes to manipulating strings and understanding how pointers work. One common problem many programmers face is counting the number of uppercase letters, lowercase letters, and digits in a given character string. In this guide, we will explore this problem, provide a solution, and explain the necessary adjustments needed to make your function work correctly.

The Problem

You may find yourself unable to get your character counting function to work as expected. The goal is to create a function that counts the number of uppercase letters, lowercase letters, and digits in a given C string. However, issues may arise, particularly related to the usage of pointers and the loop's termination condition.

Here’s a simplified example of what the problem might look like in C:

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However, this code does not work properly as written. Let’s see how we can fix it.

Our Goal: A Functional Character Counting Function

We are going to write a function named count_categories that takes a string and the addresses of three integer variables (for uppercase, lowercase, and digit counts) as parameters. The important concepts we will cover include dereferencing pointers, correctly iterating through strings, and adjusting our loop conditions.

Key Issues to Address

Dereferencing Pointers: In the original code, the counters were being incremented incorrectly. Instead of incrementing the value the pointer points to, the pointer itself was incremented. This is how to correctly increment the counts:

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Loop Termination Condition: The loop currently uses k != '\0' as the condition, which is incorrect. You need to check the value in the string at position k instead:

[[See Video to Reveal this Text or Code Snippet]]

The Corrected Function

Combining these insights, here’s the revised version of our count_categories function:

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Putting It All Together

Now that we have our function defined correctly, here is how you would call it:

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Conclusion

By addressing the issues with pointer dereferencing and the loop termination condition, you can effectively count uppercase letters, lowercase letters, and digits in a C string. Understanding how pointers and string manipulation work in C is crucial for successful programming. Now you're equipped to tackle this common problem with confidence!

For more coding tips and guides, stay tuned for our next posts!