/in/foo.c: In function 'main':
/in/foo.c:4:2: warning: implicit declaration of function 'gets' [-Wimplicit-function-declaration]
  gets(str);
  ^~~~
/in/foo.c:5:16: warning: implicit declaration of function 'strlen' [-Wimplicit-function-declaration]
  int i, j, len=strlen(str);
                ^~~~~~
/in/foo.c:5:16: warning: incompatible implicit declaration of built-in function 'strlen'
/in/foo.c:5:16: note: include '<string.h>' or provide a declaration of 'strlen'
/in/foo.c:20:3: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
   printf("%c",str[i]);
   ^~~~~~
/in/foo.c:20:3: warning: incompatible implicit declaration of built-in function 'printf'
/in/foo.c:20:3: note: include '<stdio.h>' or provide a declaration of 'printf'
/tmp/ccrs0Phr.o: In function `main':
foo.c:(.text.startup+0x16): warning: the `gets' function is dangerous and should not be used.