int[ ][ ] myArr = { {1, 2, 3}, {4}, {5, 6, 7} }; myArr[0][2] = 42; int x = myArr[1][0]; // 4

Question

Explain how 42 came

Answer 1

That code will not to compile...
I Made some corrections:
int myArr[ ][3] = { {1, 2, 3}, {4}, {5, 6, 7} };
myArr[0][2] = 42;
int x = myArr[1][0]; // 4

You need to especific the limits of all the dimensions except the first dimension