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Changing a variable is a complex question when it comes to object-oriented programming languages like C++. In this article, you'll learn the fundamentals of changing variables, which include the
What is this "const" before the data type?
const int PI = 3.14159;
const” is a very important qualifier. You should use this qualifier for variables that should never change.
L-value or R-value concept
The following shows some examples:
int X = 1, Y = 3; X = Y + 1; // Good Y + 1 = X; // INCORRECT!
The key is for L-value:
- Variable to be modified must be put on the left side of the “=” operator.
- Operation expression should be on the right side of the “=” operator.
- Basically, any other expressions.
Caution: While the following is syntactically correct, it is bad:
Output: X = 20; Y = 20;
Besides, when the compiler produces a warning, you should always review it carefully. Never a good idea to ignore it.