In C++, What use do we have for constants instread of variables?

Question

an example would be
const double PI=3.14;
for(float x=PI;whatever;x++){
cout< }

that was just an example of using constants;

but you could do the same without using constants;
double PI=3.14;
for(int x=PI;whatever;x++){
//This would also work
}


so what use do we have of using constants for somethings instread of variables

Answer 1

Constants don't change, variables can change.

You can't mistakingly change a constant. For example like this:

if(pi=3.00){
//do something
}

If pi is a constant, you'll get an error message. If pi is a variable, you won't.

Answer 2

It's just so that no one else changes them. It also indicates to other programmers that the variable is never intended to change.

Answer 3

Variables use more memory. So if you have a large program you need to consider this.

Answer 4

Its just validation, it eliminates problems caused by changing variables.

It prevents you from accidentally changing its value and messing everything up. Its very professional. I must admit, I dont use them but I should do.