foo.c: In function 'main':
foo.c:12:5: warning: implicit declaration of function 'gets_s'; did you mean 'gets'? [-Wimplicit-function-declaration]
     gets_s(a);
     ^~~~~~
     gets
foo.c:14:10: warning: unused variable 'str' [-Wunused-variable]
     char str;
          ^~~
/tmp/ccCpnVeN.o: In function `main':
foo.c:(.text.startup+0x22): undefined reference to `gets_s'
collect2: error: ld returned 1 exit status

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