CODEWITHSUNDEEP
c
MaMba
MaMba

Reputation: 123

Why is this output of this basic C program?

Let me be judged as a Noob in programming, I have been learning obfuscated way of programming in c/c++, as the c compiler compiles a statement from the right hand side towards the left hand side.

I have the following code:

int main(){
    int x=5, y=20, z=1;
    int k = x > y < z;
    printf("%d", k);
    return 0;
}

The output returned is 1, Does this means that
x > y < z = (x>y) < z
or
x > y < z = x > (y<z)

I would love if someone would give me link to work on these skills.
Thanks and Regards.

Upvotes: 1

Views: 183

Answers (6)

Vlad from Moscow
Vlad from Moscow

Reputation: 311088

According to the C grammar (6.5.8 Relational operators)

1 relational-expression:
    shift-expression
    relational-expression < shift-expression
    relational-expression > shift-expression
    relational-expression <= shift-expression
    relational-expression >= shift-expression

1 The relational operators group left-to-right (C++ Standard :) )

And

6 Each of the operators < (less than), > (greater than), <= (less than or equal to), and >= (greater than or equal to) shall yield 1 if the specified relation is true and 0 if it is false.107) The result has type int.

Thus the initializer in this declaration

int k =x>y<z;

is equivalent to

int k = ( x > y ) < z;

As x is less than y then expression x > y yields 0 and as z is greater than 0 then the full expression yields 1.

The following operators have right-to-left-grouping:

unary operators 
conditional operator  
assignmnet and compound assignment operators

Upvotes: 2

cwfighter
cwfighter

Reputation: 502

Maybe you should know the Operator precedence and associativity. You can google or see the book <<c++ primer>>. First the operator > and < have a same precedence. Then we should use the associativity, there the operator only have left associativity. So the answer is x> y< z= (x>y)<z). I hope this can help you. Remember: 1. precedence; 2. associativity.

Upvotes: 0

Lundin
Lundin

Reputation: 214860

First you have to check operator precedence, which is easiest by looking at an operator precedence table. If such a table is decent, it will list the operators > and < in a group called relational operators. All operators in this group have the same operator precedence.

Since the operators > and < have the same precedence, the order in which the operands will get processed is determined by the associativity of that group of operators. For the relational operators, this is left-to-right. Therefore the expression is guaranteed to be processed as (x > y) < z

Upvotes: 1

Bruno Caceiro
Bruno Caceiro

Reputation: 7199

k = ( 5 > 20 ) < 1= False (0)

k = (0 < 1) = True (1)

printf (%d, k) = 1

Upvotes: 0

Elias Van Ootegem
Elias Van Ootegem

Reputation: 76433

Change z=-1 or x=0 and find out. Also change int main() to the more correct int main ( void )

Changing z = -1 will ouput 0, whereas k will be 1 if you assign it x > y == z if z = 0. So in short:

k = x > y < z;

is the same as writing

k = (x > y) < z;

left-to-right.

Upvotes: 4

Olimpiu POP
Olimpiu POP

Reputation: 5067

In C the boolean values are numerical values, so:

false -> 0 true -> != 0, hence any number that is not 0 will represent the boolean true.

So in case of your code:

int k = x > y < z;

can be split in the following way:

int k = (x > y) < z;

that will be:

int k = ( 5 > 20) < 1;

the first part evaluates to false (0 that is) then the equality will loook this way:

int k = 0 < 1;

which is true, hence

int k = 1;

Upvotes: 0

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