when do we need to pass the size of array as a parameter

Question

I am a little bit confused about pass an array in C/C++. I saw some cases in which the signature is like this

void f(int arr[])

some is lik

Answer 1

C and C++ are not the same thing. They have some common subset, though. What you observed here is that the "first" array dimension when passed to a function always results just in a pointer being passed. The "signature" (C doesn't use this term) of a function declared as

void toto(double A[23]);

is always just

void toto(double *A);

That is that the 23 above is somewhat redundant and not used by the compiler. Modern C (aka C99) has an extension here that lets you declare that A always has 23 elements:

void toto(double A[static 23]);

or that the pointer is const qualified

 void toto(double A[const 23]);

If you add other dimension the picture changes, then the array size is used:

void toto(double A[23][7]);

in both C and C++ is

void toto(double (*A)[7]);

that is a pointer to an array of 7 elements. In C++ these array bounds must be an integer constant. In C it can be dynamic.

void toto(size_t n, size_t m, double A[n][m]);

They only thing that you have to watch here is that here n and m come before A in the parameter list. So better you always declare functions with the parameters in that order.