[lqet]

AFAIK only external and static variables are default initialized in C. For all other variables, the default value is undefined, so 0 is as good a choice as any other here.

[DC-3]

Except that uninitialised memory is substantially more likely to be 0 than any other value.

[grishka]

Except sometimes it is not and forgetting to initialize a variable in C/C++ leads to very insidious bugs that no one can reliably reproduce.

[kevincox]

That's not quite true. While it is undefined 0 is a fairly common value for memory and registers meaning that your "undefined" values is likely 0 a higher than average amount of the time.

[anonymousiam]

There is also the issue that (at least on some platforms) ECC memory must be initialized before being read, or an exception will occur.

[fnord77]

if you use malloc, yes. calloc will initialize the variables