Block access the data in normal way as the other normal function do. Block can access any class variable or function variable out side it but cannot modified it.

int x= 111;

void (^printXAndY)(int) = ^(int y) {
    printf("%d %d\n", x, y);
};
printXAndY(333);

output will be :

111 333

But if you try to assing the new value to variable x. then it will not change the value. For example

int x= 111;
void (^printXAndY)(int) = ^(int y) {
     x=x+y
    printf("%d %d\n", x, y);         //  error here
};

so if you want change the value then you can user __block before the variable. for example

_block int x=111;

then it upper block will the expected result. And it will add the both variable.

111+333=444.