I can't get what the mistake in my programme is?
#include <stdio.h>
main (){
     int z,d,k,arr[20],i,temp,j,flag,n,a1=0,a2=0;
     scanf("%d",&n);
     for(i=0;i<n;i++){
                      scanf("%d",&arr[i]);
                      }
     for(i = 1; (i <= n) && flag; i++)
     {
          flag = 0;
          for (j=0; j < (n-1); j++)
         {
               if (arr[j+1] > arr[j])
              {
                    temp = arr[j];
                    arr[j] = arr[j+1];
                    arr[j+1] = temp;
                    flag = 1;
               }
          }
     }
    if(n>1){
          a1=arr[0];


       for(z=1;z<n;z++){
                           if(a1>=a2){
                                     a2+=arr[z];
                                     continue;
                                                 }
                           if(a1<a2){
                                     a1+=arr[z];
                                     continue;
                                     }


                             }
     if(a1>=a2){
               printf("%d",(a1-a2));
               }
     if(a1<a2){
               printf("%d",(a2-a1));
               }


}
if(n==1){printf("%d",a1);}
}