Check if int is between two numbers

Question

Why can t do you this if you try to find out whether an int is between to numbers   if 10  lt  x  lt  20    Instead of it  you ll have to do  if 10 lt x  amp  amp  x lt 20    which seems like a bit of overhead

User · Accepted Answer

One problem is that a ternary relational construct would introduce serious parser problems:

<expr> ::= <expr> <rel-op> <expr> |
           ... |
           <expr> <rel-op> <expr> <rel-op> <expr>

When you try to express a grammar with those productions using a typical PGS, you'll find that there is a shift-reduce conflict at the point of the first <rel-op>. The parse needs to lookahead an arbitrary number of symbols to see if there is a second <rel-op> before it can decide whether the binary or ternary form has been used. In this case, you could not simply ignore the conflict because that would result in incorrect parses.

I'm not saying that this grammar is fatally ambiguous. But I think you'd need a backtracking parser to deal with it correctly. And that is a serious problem for a programming language where fast compilation is a major selling point.

User · Answer

simplifying   a   10  b   15  c   20  public static boolean check int a  int b  int c        return a lt  b  amp  amp  b lt  c      This checks if b is between a and c

User · Answer

You are human  and therefore you understand what the term  10  lt  x  lt  20  suppose to mean  The computer doesn t have this intuition  so it reads it as    10  lt  x   lt  20    For example  if x   15  it will calculate    10  lt  x     TRUE   TRUE  lt  20          In C programming  it will be worse  since there are no True False values  If x   5  the calculation will be   10  lt  x    0  the value of False   0  lt  20    non-0 number  True   and therefore  10  lt  5  lt  20  will return True   S

User · Answer

Because that syntax simply isn t defined  Besides  x  lt  y evaluates as a bool  so what does bool  lt  int mean  It isn t really an overhead  besides  you could write a utility method if you really want - isBetween 10 x 20  - I wouldn t myself  but hey

User · Answer

The inconvenience of typing 10  lt  x  amp  amp  x  lt  20 is minimal compared to the increase in language complexity if one would allow 10  lt  x  lt  20  so the designers of the Java language decided against supporting it

User · Answer

if  10  lt  x    x  lt  20   This statement will evaluate true for numbers between 10 and 20  This is a rough equivalent to 10  lt  x  lt  20

User · Answer

It s just the syntax     lt   is a binary operation  and most languages don t make it transitive   They could have made it like the way you say  but then somebody would be asking why you can t do other operations in trinary as well    if  12  lt  x    5     Syntax is always a trade-off between complexity  expressiveness and readability   Different language designers make different choices   For instance  SQL has  x BETWEEN y AND z   where x  y  and z can individually or all be columns  constants  or bound variables   And I m happy to use it in SQL  and I m equally happy not to worry about why it s not in Java

User · Answer

You could make your own  public static boolean isBetween int a  int b  int c        return b  gt  a   c  gt  a  amp  amp  c  lt  b   c  gt  b  amp  amp  c  lt  a      Edit  sorry checks if c is between a and b

User · Answer

Because the  lt  operator  and most others  are binary operators  they take two arguments   and  true true  is not a valid boolean expression   The Java language designers could have designed the language to allow syntax like the type you prefer  but  I m guessing  they decided that it was not worth the more complex parsing rules

User · Answer

COBOL allows that  I am sure some other languages do as well    Java inherited most of it s syntax from C which doesn t allow it

[java] Check if int is between two numbers

Examples related to java

Examples related to integer

Examples related to conditional-operator