C code unknown value at output

As a begineer I write a program of adding the places of a digit.

Code:

---

#include<stdio.h>#include<conio.h>

void main()
{
clrscr();
int a,b,sum=0,e,z;
printf("Enter the digit");
scanf("%d",&a);
while(a!=0)
{
b=a%10;
sum=sum+b;
a=a/10;
}
printf("the sum is %d",sum);
getch(); }

---

but if I enter a character e.g. "w" then it gives value -26. I don't understand how this works? I also debug my code and find that it takes value -29359(0x8D51)
Instead of this if I put a=0 then at output if I enter "a" then it shows 0. How it works as I want to understand.
Anyone can help??

When you enter 'w' scanf returns 0 and leaves a with old value.
Since a is not initialized - you get garbage

Learn to check return value of used functions

PS. You can benefit from reading several FAQ entries

FAQ > main() / void main() / int main() / int main(void) / int main(int argc, char *argv[]) - Cprogramming.com

Get rid of conio.h and used something standarty FAQ > How do I get my program to wait for a keypress? - Cprogramming.com


One of the samples illustrates correct scanf usage FAQ > How do I get a number from the user (C) - Cprogramming.com

This is what you do if scanf fails FAQ > Flush the input buffer - Cprogramming.com