Is there any real reason to use "const"

Rather than just tell the compiler to not allow me to modify a variable (like I don't know what I'm doing with my program), are there any reason to use "const" variables?

Other than out of curiosity, I'm actually asking because I'm writing a transpiler and I want to know if I should support "const" (or the concept of immutability in general) or not. To me, "const" has a lot of burdens like:

"should we use it all the time if we don't want to be sure that we won't modify a variable or only for critical ones?"

"Then in this case, why not make "const" the default and use another word to allow a variable to be mutable (just like Rust and other languages)?"

Also another problem is that I don't like the way "const" is treated in functions. For example, you cannot past "const" variables to functions that take non-const parameters even if we are using variables which are ALWAYS copied (which means than modifying them will not modify the original value). This is stupid because if I want to support "const" for a function, I need to make an extra instruction to copy the value to a new non-const variable that is created inside the function and make an extra instruction. Copying a value is not a slow operation but it can be for a big struct. And in any case, it is stupid and it ........es me off....

So yeah, I would like to know as soon as possible if there are any real reasons to support something like that so I can implement it.

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Copying a value is not a slow operation but it can be for a big struct.

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Why would you want to copy a struct ? Pass it as const pointer or const ref.

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Originally Posted by thmm

Why would you want to copy a struct ? Pass it as const pointer or const ref.

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I don't mean that. But still, it turns out that I'm a complete idiot because I thought that you could not pass "const" variables in "non-const" parameters even when they were passed by copy. I thought I tried it out some at some point and it didn't worked.... Or does it truly not work in specific scenarios? Anyway this is what I thought wasn't possible to do but it is completely possible.

Code:

Code:

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#include  typedef struct {  int val; } test;

void print_and_change_val(test value) {
    value.val = 100;
    printf("The modified value is: %d\n", value.val);
}

int main() {
    const test t = { 200 };
    printf("The value inside 'main' is: %d\n", t.val);
    print_and_change_val(t);
}

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Aaaaaaaaaaaaahhhhh!!!! Why am I so stupid and lazy????? Mostly the last one....

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Originally Posted by rempas

like I don't know what I'm doing with my program

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Yes, you don't know what you're doing with your program. If you disagree, read your code from decades ago and you'll realise that it is true :p

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Originally Posted by laserlight

Yes, you don't know what you're doing with your program. If you disagree, read your code from decades ago and you'll realise that it is true :p

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Yeah, Tbh I though about it again and I probably will support "const". Tbh, it's the same way with memory management. People forget, do mistakes, program late at night etc. So I suppose it's worth it!