Why can i declare an array with a predestined size on gcc but not on visual studio c++?

Question

i was wondering why i can do this code in linux but not on visual studio? (File -> main.c)

int size;
printf(\"Size:\");
scanf(\"%d\",&size);
int vec[size];
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Answer 1

Variable length arrays(VLA) is a C99 addition to the standard and until recently Visual Studio did not support C99 and as far as I know does not support VLA. If you build this in gcc outside of C99 mode let's say in c90 mode and use the -pedantic flag it will provide a warning:

warning: ISO C90 forbids variable length array 'vec' [-Wvla]

gcc will support VLA as an extension outside of C99 mode and even in C++.

Note that C11 made VLA optional, we can see that from the draft C11 standard section 6.10.8.3 Conditional feature macros which includes the following bullet:

_ _STDC_NO_VLA_ _ The integer constant 1, intended to indicate that the implementation does not support variable length arrays or variably modified types.