() why {}

[looky]

I wondered why int main () uses these parenthesis, but then {} to begin and execute programme is this just code blocks or a c++ rule.

[jlb]

Like all functions in C++ the function main() requires a return type and parenthesis to hold the parameters, if any, and braces to denote the beginning and end of the function. And remember the function main() may have parameters.

int main(int argc, char** argv)
{

   return 0;
}

[Moschops]

All C++ functions begin like this:

RETURN_TYPE   function_name ( INPUT_PARAMETER_LIST)
{
  // function code
}

So this function:

int main()

has a RETURN_TYPE of int, it is named main, and it has no input parameters.

Here is an example of a different function:
double beans_on_toast( int a, float b)
so this function has a RETURN_TYPE of double, it is named beans_on_toast, and it has two input parameters (one is an int, named a, and the second is a float, named b).

Time to learn about functions: http://www.cplusplus.com/doc/tutorial/functions/