# BBC BASIC Programmers' Reference

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summing_20part_20of_20an_20array

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 summing_20part_20of_20an_20array [2018/03/31 13:19]127.0.0.1 external edit summing_20part_20of_20an_20array [2018/04/17 19:01] (current)tbest3112 Added syntax highlighting 2018/04/17 19:01 tbest3112 Added syntax highlighting2018/03/31 13:19 external edit 2018/04/17 19:01 tbest3112 Added syntax highlighting2018/03/31 13:19 external edit Line 2: Line 2: //by Richard Russell, October 2013 (original concept by Michael Hutton)//\\ \\  The [[http://​www.bbcbasic.co.uk/​bbcwin/​manual/​bbcwin7.html#​sum|SUM()]] function returns the sum of all the elements of an array. It may occasionally be useful to discover the sum of only **part** of an array, but BBC BASIC doesn'​t have a built-in function to do that. \\ \\  Of course it's straightforward to find the sum using a loop:​\\ ​ //by Richard Russell, October 2013 (original concept by Michael Hutton)//\\ \\  The [[http://​www.bbcbasic.co.uk/​bbcwin/​manual/​bbcwin7.html#​sum|SUM()]] function returns the sum of all the elements of an array. It may occasionally be useful to discover the sum of only **part** of an array, but BBC BASIC doesn'​t have a built-in function to do that. \\ \\  Of course it's straightforward to find the sum using a loop:​\\ ​ + total = 0 total = 0 FOR index% = first% TO last% FOR index% = first% TO last% total += array(index%) total += array(index%) NEXT NEXT + ​ where **first%** and **last%** define the range of indices (inclusive) over which the sum should be calculated.\\ \\  However this approach is relatively slow, especially if the number of elements being summed is large, and it would be desirable to have a faster method. Fortunately there is a way, although the code isn't very nice:​\\ ​ where **first%** and **last%** define the range of indices (inclusive) over which the sum should be calculated.\\ \\  However this approach is relatively slow, especially if the number of elements being summed is large, and it would be desirable to have a faster method. Fortunately there is a way, although the code isn't very nice:​\\ ​ + DEF FN_SumPartialArray(d(),​ first%, last%) DEF FN_SumPartialArray(d(),​ first%, last%) LOCAL I% LOCAL I% Line 14: Line 17: !^a() = I% !^a() = I% = SUM(a()) = SUM(a()) + ​ The array **a()** must be the same type (i.e. have the same suffix character, if any) as the array being summed.\\ \\  Note that during execution of the function the array contents are temporarily changed, so don't use this method if your program has a timer interrupt in which the array is accessed.\\ \\  If errors are trapped (using ON ERROR) and you need your program to resume execution after an error (e.g. pressing the **Esc**ape key), add a statement to ensure the array contents are restored:​\\ ​ The array **a()** must be the same type (i.e. have the same suffix character, if any) as the array being summed.\\ \\  Note that during execution of the function the array contents are temporarily changed, so don't use this method if your program has a timer interrupt in which the array is accessed.\\ \\  If errors are trapped (using ON ERROR) and you need your program to resume execution after an error (e.g. pressing the **Esc**ape key), add a statement to ensure the array contents are restored:​\\ ​ + DEF FN_SumPartialArray(d(),​ first%, last%) DEF FN_SumPartialArray(d(),​ first%, last%) LOCAL I% LOCAL I% Line 23: Line 28: !^a() = I% !^a() = I% = SUM(a()) = SUM(a()) +
summing_20part_20of_20an_20array.txt · Last modified: 2018/04/17 19:01 by tbest3112

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