foo.cc: In function 'int main()':
foo.cc:7:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %d",&L, &M);   //输入L和M  
     ~~~~~^~~~~~~~~~~~~~~~
foo.cc:11:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d %d", &b[i], &b[i+1]);  
         ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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