Sams Teach Yourself C in 21 Days

of errors can result when the proper conversion isn’t applied. The following sections

cover C’s automatic and explicit type conversions.

Automatic Type Conversions ........................................................................

As the name implies, automatic type conversions are performed automatically by the C

compiler without any action on your part. However, you should be aware of what’s going

on so that you can understand how C evaluates expressions.

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Note Automatic type conversion is often referred to as implicitconversions.

Type Promotion in Expressions

When a C expression is evaluated, the resulting value has a particular data type. If all the

components in the expression have the same type, the resulting type is that type as well.

For example, if xandyare both type int, the following expression is type intalso:

x + y

What if the components of an expression have different types? In that case, the expres-

sion has the same type as its most comprehensive component. From least-comprehensive

to most-comprehensive, the numerical data types are

char

short

int

long

long long

float

double

long double

Thus, an expression containing an intand a charevaluates to type int, an expression

containing a longand a floatevaluates to type float, and so on.

When creating expressions, the compiler uses two variables or values at a time. For

example, if you have the expression:

Y + X * 2

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