Difference - Sum of Odd and Even Digits

Given a maximum of hundred digits as the input. The program must print the difference between the sum of odd and even digits as the output. If the input is not a valid number, then print Invalid as the output.

Example Input/Output 1:
Input:
118745913

Output:
15

Explanation:
The sum of odd digits is 27 (1, 1, 7, 5, 9, 1 and 3).
The sum of even digits is 12 (8 and 4).
So the difference is 27-12 = 15.
Hence the output is 15

Example Input/Output 2:
Input:
235468173645

Output:
-6

Example Input/Output 3:
Input:
76320Afk384

Output:
Invalid

Note: The invalid number may contain white spaces.

Solution :-

#include<stdio.h>

int main()

{

    char str[1000];

    scanf("%[^\n]s",str);

    

    int len=strlen(str),flag=0,even=0,odd=0;

    

    for(int i=0;i<len;i++)

    {

        if(isalpha(str[i]) || str[i]==' ' || isalnum(str[i])==0)

        {

            flag=1;

            break;

        }

        

        int a=str[i]-48;

        

        if(a%2==0)

        {

            even=even+a;

        }

        else

        odd=odd+a;

        

    }

    

    if(flag==1)

    {

        printf("Invalid");

    }

    else

    {

        printf("%d",odd-even);

    }

    

}