Why do you define variables before clear screen function in c?

Answer 1

Variables need only be defined before they are actually used, so there is no need to define them before calling any functions that don't actually use them, including clear screen functions. However, by moving all the declarations to the top of the function, and sorting them in descending order of size, you minimise memory consumption by eliminating any unnecessary padding for alignment purposes.

For example, suppose your function uses the following variables in this order:

char ch1;

int i1;

char ch2;

int i2;

char ch3;

int i3;

char ch4;

int i4;

Assuming an int is 4 bytes, this will consume up to 32 bytes in total, because the int variables should ideally be aligned upon 32-bit boundaries. Thus each char variable wastes 3 bytes. By sorting them from largest to smallest, you reduce the consumption to just 17 bytes:

int i1;

int i2;

int i3;

int i4;

char ch1;

char ch2;

char ch3;

char ch4;

Saving just 15 bytes for one function may seem insignificant, but when applied to every function those savings can be quite substantial. The more memory you save, the smaller your code will be, and therefore the quicker it will execute.

The only problem with doing this is that variables are then scoped to the function, rather than to the statement bodies that actually use them. However, once a function has been fully debugged, it makes sense to optimise its memory consumption and then test one more time to ensure no bugs have crept in.