1. Repetition (While Loop) LAB 9
ICS 101 Lab
Hossain Arif
ICS Dept

2. Repetition
DO Loops
Last LAB
WHILE Loops
This LAB

3. WHILE Loop Informal representation
WHILE condition EXECUTE THE following
BLOCK OF STATEMENTS
FORTRAN does not have explicit WHILE statement

4. WHILE Loop WHILE Loop can be written as follows: n IF (condition) THEN
Block of statements
GOTO n
ENDIF

5. Example Consider this program – calculates average of 6 numbers
REAL X1, X2, X3, X4, X5, X6
REAL SUM, AVG
READ*, X1
READ*, X2
READ*, X3
READ*, X4
READ*, X5
READ*, X6
SUM = X1 + X2 + X3 + X4 + X5 + X6
AVG = SUM / 6.0
PRINT*, AVG
END

6. Example (Cont) Using WHILE loop REAL X REAL SUM, AVG INTEGER K
15 IF ( K .LT. 6 ) THEN
READ*, X
SUM = SUM + X
K = K + 1
GOTO 15
ENDIF
AVG = SUM / 6.0
PRINT*, AVG
END

7. Example(2) REAL WEIGHT READ*, WEIGHT 11 IF ( WEIGHT .NE. -1.0 ) THEN
IF ( WEIGHT .LT. 0 .OR. WEIGHT .GE. 400 ) THEN
PRINT*, ‘Weight is OUT of range’
ELSEIF ( WEIGHT .LT. 65 ) THEN
PRINT*, ‘LIGHT-WEIGHT’
ELSEIF ( WEIGHT .LT. 85 ) THEN
PRINT*, ‘MIDDLE-WEIGHT’
ELSE
PRINT*, ‘HEAVY-WEIGHT’
ENDIF
GOTO 11
END

8. Nested WHILE Loops WHILE Loops can be nested
Inner loop must start after outer loop and must finish before it
You can have as many nested loops as needed

9. Implied Loops Used in READ and PRINT statements
Implied Loop can be written as follows:
READ*, (list of variables, index = initial, limit, increment)
PRINT*, (list of expressions, index = initial, limit, increment)
The same DO loops rules are applied

10. Implied Loop Example What will printed by this line:
PRINT*, (K, K = 1, 10, 1)
Output:

11. Exercise(1)
Using While loop, write a FORTRAN program that calculates the summation of all odd numbers less than or equal to NUM
… + NUM
Ask the user for the value of NUM.