I know this kind of a dumb question but Im pretty new to guitar. I broke my first string the other day and I bought new ones to fix it today but I couldnt get the proper string to sound right and I overtightened it and broke my only extra string. D'OH! Tomorrow I will get new ones again and I was wondering if I should just restring the whole guitar when I get new strings.Thank you all.
(Gear in profile)

Yes I do like metal, no I'm not a close minded idiot.
I always do. It keeps them all equal. If you want to keep the old ones as backups, that's fine. The only time you should only change one is if you break it in concert.
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Skepto > Oxygen
yeah, keep a backup for emergencys like that so you could throw a backup on for a day or two but if you dont use the same strings then it just wont sound right and it will be unequil
When I get a new set, I always change them all, but I make sure to save the old ones, no matter how old, just so that incase on breaks I'll have spares until I have the time/money to buy new ones.