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275*+ is a valid input, so the problem would be in your solution. Try the Troubleshooting guide.

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I tried doing this and it doesn't work. adding '\0' per number onto the string.
Also even hardcoding a return of the first answer doesn't get it right, throws an error even though the line before prints out the exact answer..

I tried this and it didn't work, why would adding null's to a string solve this issue anyway?

I cout my output before returning the string and it's identical to the answer, but throws an error for some reason.

I've already solve this problem before and I know my code coverts it correctly, I cout my postFix string and it's accurate but it gives me a huge error on case one 275*+ not sure what the issue is but it's very frustrating. I attached the error below, even returning a hardcoded "275*+" gives me an error for some reason, not sure what's going on.

UndefinedBehaviorSanitizer:DEADLYSIGNAL
==1==ERROR: UndefinedBehaviorSanitizer: SEGV on unknown address 0x0000000001ff (pc 0x000000425861 bp 0x000000000003 sp 0x7fff796e5570 T1)
==1==The signal is caused by a READ memory access.
==1==Hint: address points to the zero page.
==1==WARNING: invalid path to external symbolizer!
==1==WARNING: Failed to use and restart external symbolizer!
#0 0x425860 (/workspace/test+0x425860)
#1 0x428723 (/workspace/test+0x428723)
#2 0x426f0e (/workspace/test+0x426f0e)
#3 0x426a98 (/workspace/test+0x426a98)
#4 0x42666b (/workspace/test+0x42666b)
#5 0x42b325 (/workspace/test+0x42b325)
#6 0x425d8d (/workspace/test+0x425d8d)
#7 0x7fb54e436b96 (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
#8 0x4044d9 (/workspace/test+0x4044d9)

UndefinedBehaviorSanitizer can not provide additional info.
==1==ABORTING