Blocks in Programming: Units of Scope and Execution

In programming theory, a block is a piece of code that stands as a unit. Often enough, variables in a block are invisible or inaccessible to other blocks.

Blocks are often denoted by curly braces:

{
  var x = 3;
  var y = x + 2;
}

{
  print(x); // ERROR: X has not been declared in this block
}

The visibility of a variable is called its scope. In the code above, print(x); fails to compile because x is out of scope.

By the by, an enclosed block shares the variables in the enclosing scope:

{
  var x = 3;
  var y = x + 2;
  {
    print(x); // OK
  }
}

Blocks are good for organizing code into sections.

Two languages where blocks behave as decribed here are:

• the C programming language, and
• the C++ programming language.