In for (int val :arr), what does the colon mean? [duplicate]

Answer 1

It is called range loop.

int arr[] = { 1, 2, 3 };
for (int val : arr)
   cout << val;

works the same as:

int arr[] = { 1, 2, 3 };
for (int i=0;i<sizeof(arr)/sizeof(int);i++)
{
   int val=arr[i];
   cout << val;
}

But range loop can do far more.

It simply means loop through all members. Keep in mind some classes can have a complicated iterator and a range for runs through an array in a clean way. Also, notice it is a c++11 feature.