If every operand in a numeric expression is of the same data type, the result is also of that type.
If operands of different data types are combined in an expression, the evaluation of that expression and the data type of the resulting value depend on the ranking associated with each data type. The following table shows the ranking assigned to each data type:
Data Type  Ranking 

LOGICAL(1) and BYTE  Lowest 
LOGICAL(2)  . 
LOGICAL(4)  . 
LOGICAL(8)[1]  . 
INTEGER(1)  . 
INTEGER(2)  . 
INTEGER(4)  . 
INTEGER(8)[1]  . 
REAL(4)  . 
REAL(8)[2]  . 
REAL(16)[3]  . 
COMPLEX(4)  . 
COMPLEX(8)[4]  Highest 
[1] Alpha only

The data type of the value produced by an operation on two numeric operands of different data types is the data type of the highest ranking operand in the operation. For example, the value resulting from an operation on an integer and a real operand is of real type. However, an operation involving a COMPLEX data type and a DOUBLE PRECISION data type produces a DOUBLE COMPLEX result.
The data type of an expression is the data type of the result of the last operation in that expression, and is determined according to the following conventions:
1/4 + 1/4 + 1/4 +
1/4
is 0, not 1.
Y = (I
/J)*X
, an integer division operation is performed on I
and J, and a real multiplication is performed on that result and
X.
If any operand is a higherprecision real (REAL(8) or REAL(16) ) type, all other operands are converted to that higherprecision real type before the expression is evaluated.
When a singleprecision real operand is converted to a
doubleprecision real operand, loworder binary digits
are set to zero. This conversion does not increase
accuracy; conversion of a decimal number does not produce a
succession of decimal zeros. For example, a REAL variable
having the value 0.3333333
is converted to
approximately 0.3333333134651184D0
. It is not
converted to either 0.3333333000000000D0
or
0.3333333333333333D0
.
These rules also generally apply to numeric operations in which
one of the operands is a constant. However, if a real or complex
constant is used in a higherprecision expression, additional
precision will be retained for the constant. The effect is as if a
DOUBLE PRECISION (REAL(8)) or REAL(16)
(VMS, U*X) representation of the constant were
given. For example, the expression 1.0D0 +
0.3333333
is treated as if it is 1.0D0 +
0.3333333000000000D0
.