A complex datum is an approximation of a complex number. The complex data type, COMPLEX, which defaults to a synonym for COMPLEX*8, is a pair of REAL*4 values that represent a complex number. The first element represents the real part and the second represents the imaginary part.
The default size for a COMPLEX item (no size specified) is 8 bytes. The default alignment is on 4-byte boundaries. However, these defaults can be changed by compiling with certain special options (see "Size and Alignment of Data Types ").