Lesson 2.5. Variables initialization

Syntax

There are several ways to declare and initialize variables:

Simple declaration

float x;

Declaration and initialization

float x=8.5;

Declaration, then initialization

float x;
x=8.5;

Declaration of several variables

float x, y, z;

Declaration and initialization of several variables. This is the most popular solution. One usually tries to group together similar or related variables.

float x=8.5, y=-3.2, z;

Note that the last variable z is not initialized.

Uninitialized variable

Consider the following program. What does it display?

float x;
printf ("%f", x);

One would naturally think that the program would display zero and this will often be the case, but unfortunately ... not always! This makes the uninitialized variables a particularly devious problem, since it will work most of the time.

An uninitialized variable will take the value previously stored in the same memory location. This will often be zero, but not always. The variables used without being initialized is a problem that causes many bugs that are difficult to diagnose. This phenomenon has a dedicated Wikipedia page.

Quiz

How to declare several variables on the same line?

int x; int y;

int x, y;

int x; y;

int x, int y;

Check

How to initialize a variable on the same line as its declaration?

float x = 7.3;

float x ; x = 7.3;

float 7.3 = x;

It is not possible

Check

How to declare an integer and a float in the same instruction?

int a, float b;

int float a b;

int,float a, b;

It is not possible

Check

What value will an uninitialized variable have?

Zero

It won't compile

The previous value in the memory

The program will ask the user for a value

Check

**What does the following program display?

int zero;
printf ("%d", zero);

It won't compile

Nothing

We can't tell

Check

Lesson 2.4 Summary Lesson 2.6

Lesson 2.5. Variables initialization

Syntax

Uninitialized variable

Quiz

See also