C/C++: Is this undefined behavior? (2D arrays)

Question

Is it undefined behavior if I go through the elements of a 2D array in the following manner?

int v[5][5], i;

for (i = 0; i < 5*5; ++i) {
     v[i] = i;
}         


        

Answer 1

Here v[i] stands for integer array of 5 elements.. and an integer array is referenced by an address location which depending on your 'c' compiler could be 16 bits, 32 bits...

so v[i] = i may compile in some compilers.... but it definitely won't yield the result u are looking for.

Answer by sharptooth is correct v[i][j] = i... is one of the easiest and readable solution..

other could be

int *ptr;
ptr = v;

now u can iterate over this ptr to assign the values

for (i = 0; i < 5*5; i++, ptr++) {
     *ptr = i;
}