Question/ doubt about something in C

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ToThePillory@reddit

Give it a go.

Or Google it.

As a programmer, a habit you need to form is solving problems yourself.

Don't ask people here, go and find out for yourself.

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Budget_Putt8393@reddit

There are also "code standards" that companies/organizations adopt or follow. There is a chance that your professor believes that code missing an else is harder to follow/understand in the long run.

What they should have said is "you should not skip the else". But, as the compiler pointed out, it is a preference rather than a requirement.

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aqua_regis@reddit

Try it. Write some code with and without it, compile it, run it.

Then, report back your findings.

This is the best way to learn. Try before asking. Experiment. Play around.

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Zedy28@reddit (OP)

I did, I just needed confirmation because my teacher said it’s mandatory, but when I try it for myself it works even without else

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nerd4code@reddit

There are three kinds of context for if:

if(cond) {  // Case 1
    …X…
} else  {
    …Y…
}

if(cond)    // Case 2
    {…X…}
…Y…

if(cond) {  // Case 3
    …X…
    goto somewhere;
}
…Y…

Case 1 is most appropriate where either outcome of cond is reasonable.

Case 2 is used0 to take some special action if cond, and then run some code regardless.

Case 3 might be used with any control transfer statement, infinite loop, or nonreturning function call (e.g., break, continue, return, longjmp, exit, abort, for(;;) something();), and should be preferred for error, unusual/unexpected, or one-off cases in order to get them out of the way and resume focus on more important cases. Treat else as subdividing the reader’s attention.

You can restructure any if-per-se into an if-else, of course—e.g., Case 2 is just

if(cond) {
    …X…
    …Y…
}
else {
    …Y…
}

but there’s no reason to do that as a human, unless it’s on the way to some grander refactoring. And vice versa, Case 1 might become

    if(cond) {…X…; goto skip;}
    …Y…
skip:   (void)0;

or

    if(!cond) {…Y…; goto skip;}
    …X…
skip:   (void)0;

Now, if you use a conditional expression (cond ?ifyes : ifno), then you do always need the “else”/ifno branch, because otherwise the expression might have no value. (Elder GNU-dialect compilers would actually let you omit the “then”/ifyes as a ?: b, but only as a shorthand for a ? a : b, but that’s nonstandard and mostly not supported any more.)

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captainAwesomePants@reddit

You will sometimes run into disagreements between what people tell you and what seems to be the case. When this happens, what the compiler itself does is ultimately true (you can't convince the compiler that it's wrong), but you have another weapon: the language spec. Most programming languages have some standards body describing how the language works in minute detail, and C is definitely no exception. For example, here's a PDF containing a fairly up to date C language spec: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2310.pdf

If you head to page 109 (section 6.8.4), you'll find the description of how if statements work. They are described using this grammar:

selection-statement:
    if ( expression ) statement
    if ( expression ) statement else statement
    switch ( expression ) statement

That means that, in C, an if statement can either take the form if (expression) statement, or it can take the form of if (expression) statement else statement. A statement is a bit tougher to describe, but basically it's either a single command ("printf()") or it's several commands with curly braces around it.

Anyway, you can either just know that your teacher is wrong (or that you misunderstood what they were saying), or you could, if you wanted to start a fight, bring the spec to the teacher.

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aqua_regis@reddit

There you have your answer.

Either your teacher is wrong or you tore it out of context.

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if (something) {
   printf("Welcome!\n");
}
printf("How are you?");

That's perfectly legal!