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A program initializes a variable x when it first stores a value into x. For example, in
int y;
y = 1;
the second line initializes y to 1. (Do not confuse
initializing a variable with declaring it.)
With some exceptions that we will see later, C++ does not initialize variables automatically. If you use the value of a variable x before storing any value into x, there will be a value in x, but you have no way of knowing what that value is. (The value of a variable is somewhere stored in the memory. The memory that holds x might have previously held something else. Whatever happens to be in that memory when x is declared, that is the unknown initial value of x.)
The standards for this course require a program never to use the value of a variable before the variable has been initialized.
You can initialize a variable in its declaration. For example, declaration
int z = 0;
is equivalent to
int z;
z = 0;
and
double r = 0.0, s = 0.5;
is equivalent to
double r, s;
r = 0.0;
s = 0.5;
What is the difference between declaring and initializing a variable? Answer
double x;
what value does x initially contain?
Answer
What happens if your program uses a variable before storing anything in it? Answer
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