CODEWITHSUNDEEP
cconditional-operator
user10719814
user10719814

Reputation:

How is 0 used in conditional operator in C?

Conditional operator in C is used like this: condition ? value_if_true : value_if_false
What does 0 mean when it's used in the value_if_false?

I've seen some people using it like this, for example.
a == b ? i++ : 0

It seems like it does nothing. Does this work like return 0 in other functions?

Upvotes: 2

Views: 992

Answers (5)

RobertS supports Monica Cellio
RobertS supports Monica Cellio

Reputation: 15052

The reason why someone might want to write a == b ? i++ : 0; is that s/he probably wants to have an (Caution! You are now entering an opinion-based area) easier and faster alternative to if (a == b) i++; - although this is of course opinion-based and I personally not share the same opinion.

One thing I can think of as a "blocker" at the if statement is the requirement to write the parentheses () which can be omitted by using the conditional operator instead.

"But why the 0?"

The C syntax requires a third operand for the conditional operator. Else if you would want to compile for example:

a == b ? i++;

you will get an error from the compiler:

"error: expected ':' before ';' token"

Or respectively, doing so:

a == b ? i++ : ;

would raise:

"error: expected expression before ';' token"

So they use 0 as kind of "syntax satisfier" to be able to use the conditional operator as replacement for the if statement. You could use any other numeral value here as well, but 0 is the most readable value, which signifies that it has no use otherwise.

To showcase the use at an example:

#include <stdio.h>

int main (void)
{
    int a, b, c = 4;
    a = 2;
    b = 2;

    a == b ? c++ : 0;

    printf("%d",c);
    return 0;
}

The output for c will be 5, because a == b.

Note that a == b ? i++ : 0 is different when used f.e. inside of an assignment like f.e.:

int c = a == b ? i++ : 0;

Here c is either getting assigned by i or 0, dependent upon a == b is true or not. If a == b is true, c is assigned by i. If a == b is wrong, c is assigned by 0.

Side Notes:

To view it from a technical point, ?= is called the "conditional operator". The conditional operator is one of the group of ternary operators.

If you want to learn more about the conditional operator ?=, look at ISO:IEC 9899:2018 (C18), §6.5.15 - "Conditional operator" for more information.

Upvotes: 1

Ctx
Ctx

Reputation: 18410

The ?: operator is a ternary operator, but it is not called "ternary" as some answers and/or comments here suggest. It just is the arity of the operator, just as + is a binary operator or as & is unary. If it has a name at all, it is called "Conditional Expression"-operator

It is not quite equivalent to if/else, because it is a conditional value (with the consequence, that both expressions must have the same type) in the first place, not a conditional execution. Of course, both types can be cast to make them equal.

In the case of what the OP does, a better option (if if shall not be used) is in my opinion:

a == b && i++;

which resembles a bit more logical what happens. But of course it is a matter of style.

Upvotes: 1

unalignedmemoryaccess
unalignedmemoryaccess

Reputation: 7441

In C language, ternary is shorter version of if statement and it requires both statements, if_true and if_false. It would be like this (in fact it can have multiple statements for one case, separated with comma):

Short:

condition ? if_true : if_false;

Long:

if (condition) {
    if_true;
} else {
    if_false;
}

You can also assign the value if you put something infront of condition. Short:

result = condition ? if_true : if_false;

Long:

if (condition) {
    result = if_true;
} else {
    result = if_false;
}

Now here is the trick. In C language, writing 0; is a valid statement, so your ternary becomes in longer version same as code below:

if (a == b) {
    i++;
} else {
    0; /* This is valid C statement */
}

Or if you have assignment too, it would be:

if (a == b) {
    result = i++;
} else {
    result = 0;
}

You can also do this:

int a;
/* Code here ... */
condition ? a = 5: 0;

That is effectively the same as:

if (condition) {
    a = 5;
} else {
    /* DO not touch a */
}

Upvotes: 2

Lakshitha
Lakshitha

Reputation: 1542

It helps to think of the ternary operator as a shorthand way or writing an if-else statement.

If(a == b){
    i++;
}else{
    //if assigned, return 0. Else do nothing. 
}

Upvotes: 0

Marco
Marco

Reputation: 7271

There's nothing special about 0 one could write

a == b ? i++ : 1

And it would behave the same way.

Only difference is when you assign the expression to say another variable:

int c = a == b ? i++ : 1;
// a == b -> c will be i++
// a != b -> c will be 1

However it's much cleaner to write

if (a == b) i++;

Upvotes: 0

Related Questions