If the dimension is greater than the number of initializers, the initializers are used for the first elements and any remaining elements are value initialized (§ 3.3.1, p. 98)

const unsigned sz = 3;
int ia1[sz] = {0,1,2}; // array of three ints with values 0, 1, 2
int a2[] = {0, 1, 2}; // an array of dimension 3
int a3[5] = {0, 1, 2}; // equivalent to a3[] = {0, 1, 2, 0, 0}
string a4[3] = {"hi", "bye"}; // same as a4[] = {"hi", "bye", ""}
int a5[2] = {0,1,2}; // error: too many initializers