foo.cc: In function 'int main()':
foo.cc:27:6: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
 if (j=0) j=len;//注意这里！！！
     ~^~
foo.cc:48:18: warning: format '%ld' expects argument of type 'long int', but argument 2 has type 'long long int' [-Wformat=]
 printf("%ld",a[i]);
              ~~~~^
foo.cc:9:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
 scanf("%ld",&n);
 ~~~~~^~~~~~~~~~

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