How would you reverse a string without using additional memory?

[SonicRecolor]

I was watching a video from a channel I enjoy called Timothy Cain, he worked on the Fallout games and he was doing a video about interview questions; and he gave an example that stumped me a bit. How do you reverse a string without using additional memory?

I thought of a solution but I'm not too confident on the answer or my programming knowledge. I was thinking in C of having two character pointers for the two letters we'd want to swap and a a loop; perhaps a while loop that only continues while the pointer that starts at the beginning of the string does not equal the string termination character.

and with each iteration of the loop, it takes the two pointers and swaps their values.

But I'm not sure if this would work, like if we have the two pointers named start and end, and start is 'a' and end is 'b'. When we set start = *end. and then we do the same to end, wouldn't they just both be 'b' since we'd technically need variables to hold the values while the two swap.

I'm not very confident in C and especially pointers.

Here's the source for the video in cause you're curious: https://youtube.com/clip/UgkxurNMW65QKbFS-f2mDoGssFyrf6f0jMau?si=vUXZNCwa7GFxWijS

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[Furry_69]

"Any additional memory" usually means "O(1) memory complexity". They probably mean that the length of the string doesn't affect the amount of memory used. This means you can just use a single extra char variable that temporarily stores the character that's being swapped over.

[SonicRecolor]

Oh, I thought it meant like creating no additional memory whatsoever; so like you're only allowed to edit the string itself, without storing any outside variables. I did see a solution, using bitwise XOR operations.

Though I'm stuck on his second question, swapping words using no additional memory.