why print (sum=0) executed after take input (t)?

Question

If i take a input for loop condition then print function execute then inner loop working but one less time.

int main()
    {
        int t,n,i,sub_str_len=0,len,j=1,a[j],sum=0;
        char str[100];

        scanf("%d",&t); 

        for(i=0; i < t; i++)
        {
            gets(str);
            len=strlen(str);
            while(1 == sscanf(str + sub_str_len, "%*[^0123456789]%d%n", &a[j], &n))
            {
                sub_str_len += n;
                sum = sum + a[j];
                j++;
            }
            printf("sum= %d\n", sum);
            j=1;
            sum=0;
            sub_str_len=0;
        }

        return 0;

    }