Type Conversion:
When
constants and variables of different types are mixed in an expression, they are
all converted to the same type. The compiler converts all operands up to the
type of the largest operand, which is called “type promotion”. First, all char and short int values
are automatically elevated to int. This process is called “integral promotion”. (In C99, an
integer promotion may also result in a conversion to unsigned int) Once
this step has been completed, all other conversions are done operation by
operation in the following type promotion
order.
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long double
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double
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float
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unsigned long
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long
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unsigned int
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int
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char
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Type Promotion Order:
There
is one additional special case: If one operand is long and the other is unsigned
int, and if the value of the unsigned int cannot be represented by a
long, both operands are converted to unsigned long.
Once
these conversion rules have been applied, each pair of operands is of the same
type, and the result of each operation is the same as the type of both
operands.
For
example:
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// example type conversion
#include <stdio.h>
int main()
{
char c = `c`; /* ascii value of c is 99
*/
int i = 5;
float f =7.7f;
double d = 3.12334;
/*let we print the expression
((c / i) + (f*d) - (f + i)) in different formats
*/
printf("%d", ((c / i) + (f*d) - (f + i)));
printf("\n");
printf("%f", ((c / i) + (f*d) - (f + i)));
getchar();
return 0;
}
/* output
396452324
30.349718
*/
/*
Here in the expression ((c
/ i) + (f*d) - (f + i)),
(c/i) converted into int, (f*d)
converted in to double
& (f+i) converted in
float.The result of int, double &
float is double and so the
final result is in double.
*/
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Casts:
We
can force an expression to be of a specific type by using a cast. General
form of a cast is
where
type is a valid data type. For example, to cause the expression x/2 to
evaluate to type float, we write
Casts
are technically operators. As an operator, a cast is unary and has the same
precedence as any other unary operator.
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//example using cast
#include <stdio.h>
int main()
{
int i = 159;
printf("half of i is %f", (float)i / 2);
getchar();
return 0;
}
/*
here without the cast
(float), only an integer
division would have been
performed. The cast
ensures that the fractional
part of the answer
is displayed.
*/
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