Open Watcom FORTRAN 77 Language Reference
Open Watcom FORTRAN 77 Language Reference
Open Watcom FORTRAN 77 Language Reference
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Program Structure Control Statements<br />
The presence of the "..." in the above formats indicates that the ELSE IF statement may be repeated as<br />
often as desired. If the value of logical-expression-1 is true in case (a), the block of statements<br />
following the IF statement up to the first ELSE IF statement is executed, after which control passes to the<br />
statement following the END IF statement; otherwise, control will pass to the first ELSE IF statement. If<br />
the value of logical-expression-2 is true, the block of statements following the first ELSE IF<br />
statement up to the next ELSE IF statement or END IF statement is executed, after which control passes<br />
to the statement following the END IF statement; otherwise, control will pass to the next ELSE IF<br />
statement, if there is one, or directly to the statement following the END IF statement. When the ELSE<br />
statement is used, as in case (b), and the values of all the logical expressions in the IF and ELSE IF<br />
statements are false, the block of statements following the ELSE statement is executed and then control<br />
passes to the statement following the END IF statement. An optional block label may be specified with<br />
the IF statement (see the CYCLE, EXIT or QUIT statement for more information).<br />
Examples follow which illustrate the use of the two formats.<br />
Example:<br />
IF( I .EQ. 0 )THEN<br />
PRINT *, ’I IS ZERO’<br />
ELSE IF( I .GT. 0 )THEN<br />
PRINT *, ’I IS GREATER THAN ZERO’<br />
END IF<br />
If variable I is zero when the IF statement is executed, the string I IS ZERO will be printed and the<br />
statement following the END IF statement will be executed. If variable I is not zero when the IF<br />
statement is executed, control will pass to the ELSE IF statement. If variable I is greater than zero, the<br />
string I IS GREATER THAN ZERO will be printed and the statement following the END IF statement<br />
will be executed. If variable I is less than zero then nothing would be printed and control passes from the<br />
ELSE IF statement to the statement following the END IF statement.<br />
Example:<br />
IF( A .GT. B )THEN<br />
PRINT *, ’A GREATER THAN B’<br />
A = A - B<br />
ELSE IF( A .LT. B )THEN<br />
PRINT *, ’A LESS THAN B’<br />
A = B - A<br />
ELSE<br />
PRINT *, ’A EQUAL TO B’<br />
A = 0.0<br />
END IF<br />
If the value of variable A is greater than the value of variable B when the IF statement is executed, the<br />
string A GREATER THAN B will be printed and variable A will be assigned the value of the expression A<br />
- B. Control will then pass to the statement following the END IF statement.<br />
If the value of variable A is not greater than the value of variable B when the IF statement is executed,<br />
control passes to the ELSE IF statement. If the value of variable A is less than the value of variable B,<br />
the string A LESS THAN B will be printed and variable A will be assigned the value of the expression B<br />
- A. Control will then pass to the statement following the END IF statement.<br />
If the value of variable A is not less than the value of variable B when the ELSE IF statement is executed,<br />
the string A EQUAL TO B will be printed and variable A will be assigned the value zero. Control will<br />
pass to the statement following the END IF statement.<br />
ELSE IF 195
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