Question: My guess is it just made parsing easier, but I can't see exactly why.

So what does this have ...

```
do
{
  some stuff
}
while(test);

more stuff

```

that's better than ...

```
do
{
  some stuff
}
while(test)

more stuff

```

Answer: 
It's because while statements are valid within a do-while loop.

Consider the different behaviors if the semicolon weren't required:

```
int x = 10;
int y = 10;

do 
  while(x > 0)
    x--;
while(x = y--);

```
In C/C++ whitespace don't contribute to structure (like e.g. in python). In C/C++ statements **must** be terminated with a semicolon. This is allowed:

```
do
{
  some stuff; more stuff; even more stuff;
}
while(test);

```