Sum of Digits

Routine Summary

Returns the sum of digits of a number.

Inputs

X - the number you want

Outputs

Ans - the sum of X's digits

Variables Used

X, Ans

Calculator Compatibility

TI-83/84/+/SE

Author

DarkerLine

URL: United TI

````:sum(int(10fPart(Xseq(10^(-I-1),I,0,log(X`
```

With our number stored in X, we loop through each of the digits of the number starting from the right using the seq( command. We get the respective digit by raising the number to the respective power of 10 and then multiplying the result by 10. The digits are returned separately in a list, and then we take the sum of them using the sum( command.

For example, if the number is 1234, we get a list of {1,2,3,4}, which then returns a sum of 10. You should note, though, that this routine only works with positive and negative whole numbers, and will return incorrect results if you try to use a decimal number. You could fix this problem by using the code below instead:

````:abs(E13(X/10^(int(log(abs(X+not(X→X`
```

Here, we obtain the appropriate power of ten by which to divide the number so as to leave only one digit to the left of the decimal point. Because a real variable may contain only 14 digits, the answer is multiplied by 10^13 to guarantee the removal of any fractional part. From taking the absolute value of this new result, our number can be safely entered into the routine above.

Note: It should be understood that this routine is only capable of adding the first 14 digits of a number. An input of π, for instance, would return 69 even though the sum of all digits of π is infinite.

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