foo.c: In function 'main':
foo.c:11:28: warning: 'b' is used uninitialized [-Wuninitialized]
   11 |                 if(a[n]<=(b+30)){
      |                          ~~^~~~
foo.c:5:13: note: 'b' was declared here
    5 |         int b;
      |             ^

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