Assignment Statement (Executable) [ HP FORTRAN 77/iX Reference ] MPE/iX 5.0 Documentation
HP FORTRAN 77/iX Reference
Assignment Statement (Executable)
The assignment statement evaluates an expression and assigns the
resulting value to a data item. There are four kinds of assignment
statements:
* Arithmetic
* Logical
* Character
* Aggregate
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| | | |
| Item | Description/Default | Restrictions |
| | | |
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| | | |
| variable1 | Variable or array element. | If arithmetic assignment, |
| array_element | | type must be integer, real, |
| scalar_record_field_name | | or complex. |
| substring | | |
| | | If logical assignment, type |
| | | must be logical. |
| | | |
| | | If character assignment, |
| | | type must be character. |
| | | |
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| | | |
| expression | The expression to which the | If the variable or array |
| | variable or array element is | element is arithmetic, |
| | being assigned. | expression must be an |
| | | arithmetic expression; if |
| | | logical, expression must of |
| | | type logical; if character, |
| | | expression must be of type |
| | | character. |
| | | |
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| | | |
| aggregate1 | A record with one or more | Both must be declared with |
| aggregate2 | fields. | the same structure. |
| | | |
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Arithmetic Assignment Statement (Executable)
Semantics
If the type of the variable on the left of the equal sign differs from
that of the expression, type conversion takes place. The expression is
evaluated and the result is converted to the type of the variable on the
left. The converted result then replaces the current value of the
variable. Conversion rules for the assignment statement are shown in
Table 3-3 , followed by examples in Table 3-4 . See also Table 2-4
.
Table 3-3. Type Conversion for Arithmetic Assignment Statements
of the Form: Variable = Expression
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| | | | |
| Rule | Variable Type | Expression Type | Rules |
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| | | | |
| a. | INTEGER*k | INTEGER*n | If k >= n, assign INTEGER*k. If k < n, |
| | (or LOGICAL*k) | | assign least significant byte or half word |
| | (see Note 3) | | to variable. See Note 1. |
| | | | |
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| | | | |
| b. | INTEGER*k | REAL*n | Truncation. |
| | (or LOGICAL*k) | | |
| | (see Note 3) | | |
| | | | |
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| | | | |
| c. | INTEGER*k | COMPLEX*8 | Real part is REAL*4. Apply rule b to real |
| | (or LOGICAL*k) | | part. Imaginary part is not used. |
| | (see Note 3) | | |
| | | | |
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| | | | |
| d. | INTEGER*k | COMPLEX*16 | Real part is REAL*8. Apply rule b to real |
| | (or LOGICAL*k) | | part. Imaginary part is not used. |
| | (see Note 3) | | |
| | | | |
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| | | | |
| e. | REAL*k | INTEGER*n | Float and assign REAL*k. See Note 2. |
| | | | |
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| f. | REAL*k | REAL*n | Round and assign REAL*k. |
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| | | | |
| g. | REAL*k | COMPLEX*8 | Real part is REAL*4. Apply rule f to real |
| | | | part. Imaginary part is not used. |
| | | | |
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| | | | |
| h. | REAL*k | COMPLEX*16 | Real part is REAL*8. Apply rule f to real |
| | | | part. Imaginary part is not used. |
| | | | |
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| | | | |
| i. | COMPLEX*8 | INTEGER or REAL | Convert to REAL*4 by rule e or f and assign |
| | | | to real part. Imaginary part = 0. |
| | | | |
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| | | | |
| j. | COMPLEX*16 | INTEGER or REAL | Convert to REAL*8 by rule e or f and assign |
| | | | to real part. Imaginary part = 0. |
| | | | |
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| | | | |
| k. | COMPLEX*k | COMPLEX*n | Apply rule f to real and imaginary parts. |
| | | | |
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Notes for Table 3-3
1. If the value of the expression is between -32768 and +32767, the
result of the conversion from INTEGER*4 to INTEGER*2 is correct;
otherwise, the result is incorrect.
2. When converting from INTEGER*4 to REAL*4, the precision can be
lost because INTEGER*4 holds 31 significant bits, while the number
of significant bits for REAL*4 is system dependent. Refer to
Chapter 10 for more details on data representation.
3. As an extension to the ANSI 77 standard, logical variables
appearing in an arithmetic context may be treated as integer
variables, depending upon compiler directives.
In Table 3-4 , k and n represent examples of possible combinations of
byte sizes for the particular data type. For example, if the variable is
INTEGER*k and the expression is REAL*n, k can be 2 or 4, while n can be
4, 8, or 16. This represents six possible combinations of byte sizes.
Table 3-4. Examples of Type Conversions for Arithmetic Assignment Statements
of the Form: Variable = Expression
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| | | | | |
| Rule | Variable Type | Variable Value | Expression Value | Expression Type |
| | | | | |
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| | | | | |
| a. | INTEGER*4 | 542 | 542 | INTEGER*2 |
| | or LOGICAL*4 | | | |
| | | | | |
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| | | | | |
| a. | INTEGER*2 | Undefined (see Note | 86420 | INTEGER*4 |
| | or LOGICAL*2 | 1). | | |
| | | | | |
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| b. | INTEGER*2 | 3 | 3.842 | REAL*4 |
| | or INTEGER*2 | | | |
| | | | | |
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| b. | INTEGER*2 | 373 | 373.7Q0 | REAL*16 |
| | or LOGICAL*2 | | | |
| | | | | |
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| | | | | |
| c. | INTEGER*2 | 502 | (5.0297E2,1.27E-5) | COMPLEX*8 |
| | or LOGICAL*2 | | | |
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| d. | INTEGER*4 | -48170 | (-4.817D4,1.0096D7) | COMPLEX*16 |
| | or LOGICAL*4 | | | |
| | | | | |
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| e. | REAL*4 | 59. | 59 | INTEGER*2 |
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| f. | REAL*8 | 10.D+09 | 10.E+09 | REAL*4 |
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| f. | REAL*4 | 1.7014E+38 | 1.7014118344D+38 | REAL*8 |
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| h. | REAL*4 | 8.425 | (8.425,-6.02E-2) | COMPLEX*8 |
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| h. | REAL*8 | 2.2964D-8 | (2.2964D-8,6.2881D-4) | COMPLEX*16 |
| | | | | |
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| h. | REAL*16 | 3.57Q297 | (3.57D297,-1.0D32) | COMPLEX*16 |
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| i. | COMPLEX*8 | (50.0,0) | 50 | INTEGER*2 |
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| i. | COMPLEX*8 | (25.0,0) | 25 | REAL*4 |
| | | | | |
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| j. | COMPLEX*16 | (14.23D-17,0.) | 14.23E-17 | REAL*4 |
| | | | | |
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| j. | COMPLEX*16 | (1.0D28,0.0D0) | 1.0000000000000000000635Q28| REAL*16 |
| | | | | |
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| | | | | |
| k. | COMPLEX*8 | (-4.817E4,1.0096E7 | (-4.817D4,1.0096D7) | COMPLEX*16 |
| | | | | |
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| | | | | |
| k. | COMPLEX*16 | (8.425D0,_6.02D-2) | (8.425,-6.02E-2) | COMPLEX*8 |
| | | | | |
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Examples Notes
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total = subtotal + tally Defines the value of total as the value of subtotal
+ tally.
sum = sum + 1 Replaces the value of sum with the value of sum +
1.
rate(10) = new_rate * 5 Defines the 10th element of the array rate as the
value of new_rate multiplied by 5.
Logical Assignment Statement (Executable)
Semantics
Both the variable and the expression must logical types in a logical
assignment statement.
Examples Notes
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LOGICAL log1 log1 is assigned the value .TRUE. because i
i = 10 equals 10.
log1 = i .EQ. 10
LOGICAL log_res, flag_set log_res is assigned the value .FALSE.
num = 100 because num is not greater than 200.
flag_set = .TRUE.
log_res = NUM .GT. 200 .AND. flag_set
Character Assignment Statement (Executable)
Semantics
If the length of the variable is greater than the length of the
expression, the value of the expression is left-justified in the
variable, and blanks are placed in the remaining positions. If the
length of the variable is less than the length of the expression, the
value of the expression is truncated from the right until it is the same
length as the variable.
Examples Notes
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CHARACTER*6 name The variable name is assigned the character
CHARACTER*4 instrument(6),k string "CYBELE".
name = 'CYBELE'
:
k = 'horn' The fifth element of the array instrument
instrument(5) = k is assigned the character string "horn".
:
instrument(4) = name(3:5) // 'L' The fourth element of the array instrument
is assigned the character string "BELL".
CHARACTER*21 employee_name The variable employee_name is assigned the
employee_name = 'GEORGE WASHINGTON' value "GEORGE Delta WASHINGTON Delta Delta
Delta Delta ".
CHARACTER security_code*4 The variable security_code is assigned the
security_code = 'ZXYwvu' value "ZXYw".
CHARACTER address*20 The first through fourth characters of the
address (1:4) = '1645' variable address are assigned the value
address(6:14) = 'First St.' "1645" and the sixth through fourteenth the
value "First St.".
Aggregate Assignment Statement (Executable)
Semantics
The field values of the aggregate on the left side of the equal sign are
assigned to the corresponding fields of the aggregate on the right side
of the equal sign. The two aggregates must be declared with the same
structure name.
Examples Notes
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STRUCTURE/student/ A structure named student is declared with
CHARACTER*32 name two fields, name, a 32-byte character type,
INTEGER*2 age and age, a 2-byte integer type.
END STRUCTURE
STRUCTURE/teacher/ A structure named teacher is declared with
CHARACTER*32 name two fields whose names and data types are
INTEGER*2 age identical to the structure student.
END STRUCTURE
RECORD/student/math_student Two records named math_student and
RECORD/student/english_student english_student are declared using the
RECORD/teacher/math_teacher structure named student. One record named
math_teacher is declared using the
structure named teacher.
math_student = english_student This is a valid aggregate assignment
statement, since both variables were
declared with the same structure name.
math_student = math_teacher This is an illegal aggregate assignment
statement, since the two variables were
declared with different structure names,
even though the two structures are
identical in form.
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