write C program to compute the numeric root - c

Question

The numeric root of x is computed as follows:
a) Compute the sum, y, of all of x’s (decimal) digits;
b) If y is greater than 10, then set x to y and go to step a). Otherwise, y is x’s numerical root.
Thus, the numeric root of 10, 202 and 875 are 1, 4 and 2, respectively.
Here is my code:
#include <stdio.h>
int main(void)
{
int x, y, index, found;
found = 0;
scanf("%d", &x);
if (x < 0)
{
printf("The input number must be nonnegative.\n");
}
else
{
y = 0;
index = x % 10;
while (found != 1)
{
while (x > 10)
{
y = y + index;
x = (x - index) / 10;
index = x % 10;
}
y = y + index;
if (y < 10)
{
printf("%d\n", y);
found = 1;
}
else
{
x = y;
}
}
}
return 0;
}
My output are always numbers like "-2147483623" etc.
Any help will be appreciated.

Answer 1

Your solution can be greatly simplified with the use of a simple function.
See the following solution using the Ada language:
with Ada.Integer_Text_IO; use Ada.Integer_Text_Io;
with Ada.Text_IO; use Ada.Text_IO;
procedure Main is
Inpt_Value : Natural;
Root : Natural := 0;
function Find_Root(X : Natural) return Natural is
Value : Natural := X;
Root : Natural := 0;
begin
while Value > 0 loop
Root := Root + (Value mod 10);
Value := Value / 10;
end loop;
return Root;
end Find_Root;
begin
Put("Enter a non-negative integer: ");
Get(Item => Inpt_Value);
Root := Find_Root(Inpt_Value);
while Root > 10 loop
Root := Find_Root(Root);
end loop;
Put_Line(Root'Image);
end Main;

Answer 2

I think that your problem is here :
if(y < 10){
printf("%d\n",y);
found = 1;
}
else{
x = y;
}
in your else statement you assign the value of x to y, but you don't change the value of y.
Maybe you should do something like this :
if(y < 10){
printf("%d\n",y);
found = 1;
}
else{
x = y;
y = 0;
index = x % 10;
}
In your entire program you don't seem to decrease or reset the value of y, that's why once the else block entered, there is no way to enter the if block, because y will increase and always be greater than 10 until an overflow happens, that's why y is negative at the end.
PS: Always use a debugger or printf statements it will help you detect such problems.