| Basic of Fortran Language |
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| Constant |
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| A constant is a number which does not change till the end of a
program. As we know in algebra 1, 2, 3,.........etc are constant
which have same value as it is given and cannot be changed. Just
like that Fortran language have also constant whose value does
not vary up to the end of a program |
| Example: |
1
1234
89.43
It is clear from the above example that the value of 1 or 1234
or 89.43 will be always same and will never change. |
| Types of constants |
| a) Integer constants |
| Whole numbers without any fractional parts are called Integer constants. All integer constant must have at least one digit without decimal point. The largest integer constant depends on the computer being used. For IBM PCs and 32 bit work stations the range is |
+ - 2147483647
If - or + sign is not given then according to the rule the sign
will be considered as positive. |
| Example: |
1
7463
+8677
-986 etc.
It is wrong to show integer constant |
| Example: |
.4 (decimal should not be given)
133.07 (decimal point is not allowed) |
| b) Real constants or Floating point constants |
| Real constant or Floating constant are same. Users should not
confuse about these name. They may have fractional parts. |
| Rules of Real Constants |
| Rule 1 |
| A Real constant in a fractional form must have at least one digit
and must be written with a decimal point. It may have either the
+ or the - sign preceding it. If a sign does not precede it then
it is assumed to be positive. |
| Example: |
1.3
74.04
-42.6 |
This means only +, - or . (decimal point) are allowed.
It is wrong to show: 1 (decimal point is must otherwise it will
be an integer constant)
It should be written as: 1.0 |
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| Rule 2 |
| A Real constant in the exponent form consists of a mantissa and
an exponent. The mantissa must have at least one digit and a decimal
point. The mantissa is followed by the latter E and the exponent.
The exponent must be an integer (without a decimal point) and
must have at least one digit. A sign for the exponent is optional. |
| Example: |
134.E04
123.0E4
-123.456E+54 etc. |
| c) Character Constants |
| A character constant is any sequence or group of characters enclosed
in apostrophes |
| The group of characters enclosed between apostrophes ('), is known
as character constant or literal constant. An apostrophes is only
a control character and it may appear in a constant as control
character |
| Example: |
'A', 'ASDF', 'RAM', 'X+Y+Z', etc
Apostrophes themselves are represented using two apostrophes.
e.g. SHIV'S FRIEND can be represented as: 'SHIV''S FRIEND' |
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