| .FOR...NEXT Statement Details. |
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| FOR...NEXT Statement Details |
|
| Syntax |
| FOR counter = start TO end [STEP increment] |
| [statements] |
| NEXT [counter [,counter...]] |
| |
| Argument Description |
| counter A numeric variable used as the loop counter. The |
| variable cannot be an array element or a record element. |
| start The initial value of the counter. |
| end The final value of the counter. |
| increment The amount the counter is incremented each time through |
| the loop. If you do not specify STEP, increment defaults |
| to one. |
| |
| A FOR...NEXT loop executes only if start and end are consistent with |
| increment. If end is greater than start, increment must be positive. |
| If end is less than start, increment must be negative. This is checked |
| at run-time by comparing the sign of (end - start) with the sign of |
| step. If both have the same sign, the FOR...NEXT loop is entered. If |
| not, the entire loop is skipped over. |
| |
| Within the FOR...NEXT loop, the program lines following the FOR |
| statement are executed until the NEXT statement is encountered. Then |
| counter is changed by the amount specified by STEP, and compared with |
| the final value, end. |
| |
| If counter is less than or equal to end, control returns to the |
| statement after the FOR statement and the process repeats. If counter |
| is greater than end, the loop is exited; execution continues with the |
| statement following the NEXT statement. (If STEP is negative, the loop |
| repeats until counter is less than end.) |
| |
| If start and end have the same value, the loop executes once, |
| regardless of the value of STEP. If STEP is zero, the loop repeats |
| indefinitely. |
| |
| Avoid changing the value of counter within the loop. Changing the |
| loop counter is poor programming practice; it makes the program |
| more difficult to read and debug. |
| |
| You can nest FOR...NEXT loops; that is, you can place a FOR...NEXT |
| loop within another FOR...NEXT loop. To ensure that the nested loops |
| work properly, give each loop a unique variable name as its counter. |
| The NEXT statement for the inside loop must appear before the NEXT |
| statement for the outside loop. The following construction is the |
| correct form: |
| |
| FOR I = 1 TO 10 |
| FOR J = 1 TO 10 |
| FOR K = 1 TO 10 |
| . |
| . |
| . |
| NEXT K |
| NEXT J |
| NEXT I |
| |
| A NEXT statement with the form |
| |
| NEXT K, J, I |
| |
| is equivalent to the following sequence of statements: |
| |
| NEXT K |
| NEXT J |
| NEXT I |
| |
| The EXIT FOR statement is a convenient alternative exit from |
| FOR...NEXT loops. See the EXIT FOR statement. |
| |
| Note: If you omit the variable in a NEXT statement, the NEXT statement |
| matches the most recent FOR statement. If a NEXT statement is |
| encountered before its corresponding FOR statement, an error |
| message is generated that reads "NEXT without FOR."the value of |
| attribute is 1. |
| |
| Differences from BASICA |
| |
| Unlike BASICA, QuickBASIC supports double-precision control values |
| (start, end, and counter) in its FOR...NEXT loops. However, if the |
| control values fall within the range for integers, you should use |
| integer control values for maximum speed. |
