Скачать или смотреть How to Fix Common Issues in Your cs50 Substitution Program

Learn how to troubleshoot and resolve input problems and bugs in your `cs50` substitution program for encryption.
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This video is based on the question https://stackoverflow.com/q/63230117/ asked by the user 'Lakshya Dugar' ( https://stackoverflow.com/u/14042036/ ) and on the answer https://stackoverflow.com/a/63230210/ provided by the user 'MikeCAT' ( https://stackoverflow.com/u/4062354/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Solving Input Problems in Your cs50 Substitution Program

In coding, especially when implementing algorithms like encryption, it’s not uncommon to encounter input problems that can leave you frustrated. One such scenario arises when you're working on the cs50 pset 2 – the substitution program. In this guide, we will address common issues that might prevent your program from prompting for input and guide you through the necessary corrections.

Understanding the Problem

In your substitution program, you’re expected to encrypt plaintext using a user-provided key via the command line. However, issues such as the program not prompting for input can throw a wrench in your development process. In examining the code structure you provided, the root cause of the problem stems from the implementation of the check function.

Main Issues and Their Solutions

Let’s examine the mistakes in your code and how to rectify them to ensure your program works seamlessly.

1. Incorrect Initialization in the Check Function

You had the inner loop initialized as follows:

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

This setup leads to always comparing the same character, resulting in a return value of 1 for the check function, indicating a failure, which prevents the input prompt from being displayed.

Solution:
Change the initialization of j to start from i + 1:

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

This adjustment allows the loop to correctly identify duplicate characters within the key.

2. Checking for NULL Key Before Measuring Length

A common oversight is measuring the length of argv[1] (the key) before ensuring it is not NULL. If c (i.e., argc) is less than 2, argv[1] will indeed be NULL, leading to potential runtime errors.

Solution:
Revise your checks to ensure that key is not NULL before measuring its length. Adjust this part of your code to look like this:

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

This ensures that the program checks essential conditions before executing further logic.

3. String Termination in Ciphertext

You also faced an issue where the printf function for displaying output could invoke undefined behavior because ctext was not properly null-terminated. This might lead to printing garbage values or causing runtime errors.

Solution:
Allocate ctext with an additional index for the null terminator and manually terminate the string:

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

Make sure to implement this before your printf statement.

Conclusion

By addressing these common pitfalls, you can enhance the functionality of your cs50 substitution program. The best practice is to always ensure proper checks and initializations before entering loops or handling string operations. Remember, debugging is a part of programming, and overcoming these challenges not only improves your code but also reinforces your understanding of programming concepts.

Happy coding, and good luck with your cs50 projects!