What is the difference between scope and block?

Question

I saw a piece of code in a book, which is as follows:

x = 10;
if(x ==10) { // start new scope
int y = 20; // known only to this block
x = y * 2;
}


        

Answer 1

They are mostly the same.

A block is some code surrounded by { and }. A scope is the part of the program where a certain thing is visible. As far as I know, all blocks create scopes - anything defined in a block isn't visible outside the block. The converse is not true.

Here are some scopes without blocks:

for(int k = 0; k < 10; k++) { // k<10 and k++ are in a scope that includes k, but not in a block.
    System.out.println(k); // this is in a block (the {})
}

for(int k = 0; k < 10; k++) // k<10 and k++ are in a scope that includes k, as above
    System.out.println(k); // but there's no block!

class Test {
    // this is a scope but not a block. Not entirely sure about this one.
    int x = 2;
    int y = x + 1; // I can access x here, but not outside the class, so the class must be a scope.
}

Answer 2

when it comes to conditions and loops if you don't specify {} then immediate following statement is the only statement that will belong to particular condition or loop

e.g.

x = 10;
if(x ==10) 
{ 
int y = 20; 
x = y * 2;
}
both lines get executes only if condition returns TRUE

x = 10;
if(x ==10) 
int y = 20;
x = y * 2; // this is not belong to if condition. therefore it will execute anyway

Answer 3

For programming languages in general, the scope of a block (also known as block scope) is just one kind of scope; see https://en.wikipedia.org/wiki/Scope_(computer_science)#Levels_of_scope.

Some languages, like Python, do not have blocks nor block scopes (but instead have function scopes, global scopes, etc.).