foo.c: In function 'zhuanhuan':
foo.c:29:18: warning: unused variable 't' [-Wunused-variable]
  int sum=0,i=0,l,t;
                  ^
foo.c: In function 'main':
foo.c:12:2: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d%s",&n,s);
  ^~~~~~~~~~~~~~~~~~