foo.c: In function 'main':
foo.c:11:6: warning: implicit declaration of function 'system' [-Wimplicit-function-declaration]
      system("pause");
      ^~~~~~
foo.c:5:3: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%s", a);
   ^~~~~~~~~~~~~~

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