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From the What's new? in CS50 2017 document: CS50 Library To be more consistent with stylistic conventions in C, we’ve renamed the functions in the CS50 Library as follows: GetChar is now get_char Get …

First, notice that the check50 result and your result have different nonsense characters at the end. Recall from the Week 2 Lecture "More on Strings" (starting around 1:18) the discussion about stri …

The problem comes because cipher is declared a char array here char cipher[strlen(plain)];, but printed out using a string (aka char*) format here printf("ciphertext: %s\n", cipher);. Remember, the t …

The output does not match the spec. This plaintext : should be this plaintext:. The same with ciphertext:. There is no space between the word and the :. While this may seem "overly strict", it is good …

It's a memory thing, as in you will get different results based on what is in memory.ctxt is declared as an array of chars. Here printf("ciphertext: %s\n", ctxt); is treating it like a string (viz th …

The problem is this cipher key BBCCEFGHIJKLMNOPQRSTUVWXYZ should not perform the encoding, it should give an error. From the spec [emphasis added]: If the key is invalid (as by not containing 26 …

When you do not supply an argument, the runtime error comes here int k = atoi(argv[1]); because argv[1] is null and atoi cannot accept null. You need to check that the user has supplied an argument be …

The good news is: it looks like your ciphering algorithm is working. Yay. The bad news is you missed a important detail in the spec. Notice the difference between what cs50 is expecting: "ciphertext …

It will. If you do not supply any command line arguments. Try it. Why is that? Recall from Week 2 > Section > Command Line Arguments argc will always be at least 1, the name of the program. When …

I don't know where you are on the "comfortable" spectrum, but I will assume that you're closer to "more" since you are trying this and you are using const. I hope I can explain it adequately. This sta …

Consider removing the typecasting, because it is essentially redundant. A char is a one-byte integer; the system does it's own internal "casting". Perhaps rewatch the caesar walkthrough. Starting arou …

The main reason for the seg fault is this string titleized_string = "";. As soon as you "set" titleized_string to "something-in-quotes" it becomes a constant. You cannot strcpy into a constant (it ha …

Your output does not match the spec. The spec says Implement a program that encrypts messages using Vigenère’s cipher, per the below. $ ./vigenere ABC plaintext: HELLO ciphertext …

It will work when constructed as in the man page. From man feature_test_macros: NOTE: In order to be effective, a feature test macro must be defined before including any header files. This can …

This is a textbook example of "undefined behaviour". It gives different results on different machines because, well, there's a bug and there is no way to predict when or how it will "work" or fail. …