foo.c: In function 'main':
foo.c:22:19: warning: unused variable 'sum3' [-Wunused-variable]
     int sum1,sum2,sum3,cnt=0,n,i,j;
                   ^~~~
foo.c:22:14: warning: unused variable 'sum2' [-Wunused-variable]
     int sum1,sum2,sum3,cnt=0,n,i,j;
              ^~~~
foo.c:22:9: warning: unused variable 'sum1' [-Wunused-variable]
     int sum1,sum2,sum3,cnt=0,n,i,j;
         ^~~~
foo.c:23:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&n);
     ^~~~~~~~~~~~~~