C# For loop index returns ascii instead of current iteration

Question

I need to make a program that calculates the factorial of a number and sums the different numbers.

I'm stuck at the point where I need to take the current number in the for loop to do it's factorial (e.g. the number 145 and I can't take the 5). I've tried the following:

for (int i = length-1; i >= 0; i--)
{
    int currentNumber = inputString[i];
    currentSum = currentSum * i;
    sum += currentSum;
}

inputString is the length of the given number. The problem is that in this way currentNumber becomes the ascii equivalent (if i = 3 currentSum becomes 51). How do I make currentSum become 3?

int currentNumber = inputString[i] - '0';

Sani Huttunen
– Sani Huttunen

2019-09-23 07:46:45 +00:00
Commented Sep 23, 2019 at 7:46 — Sani Huttunen
– Sani Huttunen, Commented Sep 23, 2019 at 7:46

Michał Turczyn · Accepted Answer · 2019-09-23 08:42:40Z

4

Alternatively you could use:

int currentNumber = int.Parse(inputString[i].ToString());

edited Sep 23, 2019 at 8:42

answered Sep 23, 2019 at 8:04

Michał Turczyn

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1 Comment

Innat3 Over a year ago

int.Parse only accepts string values, not char, this will result in a compile error unless you add .ToString() to inputString[i]

Fildor · Accepted Answer · 2019-09-23 08:25:08Z

2

I'd like to suggest an alternative:

int num = int.Parse(inputString); // Convert whole input to int
int sum = 0;

while( num != 0 ) // >0 is not enough, num could be negative.
{
    sum += num % 10;  // Sum up least significant place
    num = num / 10;   // "Decimal shift right"
}

With your example "145" this would mean:

Iteration 1:
sum += 145 % 10 => sum = 0 + 5 = 5
num = num / 10 => num = 145 / 10 = 14

Iteration 2:
sum += 14 % 10 => sum = 5 + 4 = 9
num = num / 10 => num = 14 / 10 = 1

Iteration 3:
sum += 1 % 10 => sum = 9 + 1 = 10
num = num / 10 => num = 1 / 10 = 0

num == 0 => end while , sum = 10

Disclaimer: This assumes, the input is in fact a valid integer value. I'd strongly suggest to validate that, first. "Never trust user input."

edited Sep 23, 2019 at 8:25

answered Sep 23, 2019 at 8:10

Fildor

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Comments

decPL · Accepted Answer · 2019-09-23 07:47:07Z

1

Assuming inputString is numeric only, you can get away with:

int currentNumber = inputString[i] - '0';

Short explanation: character representation of number '3' is 51, but they are in order (so '0' is 48, '1' is 49, etc.) and you can get the "numerical value" of a character by removing the offset (which is the value of '0').

answered Sep 23, 2019 at 7:47

decPL

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2 Comments

Валери Михайлов Over a year ago

This worked like a charm. I'll be using this method until my knowledge becomes enough to come up with my own. Thank you!

Flater Over a year ago

+1 for clever and reasonably readable. I would suggest commenting this code with a small explanation of what exactly is happening, something along the lines of // Converting char ASCII value to int value

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