foo.c: In function 'main':
foo.c:20:34: warning: 'count4' may be used uninitialized [-Wmaybe-uninitialized]
   20 |         printf("%.2lf%%\n",count4/n*100);
      |                            ~~~~~~^~
foo.c:9:37: note: 'count4' was declared here
    9 |         double count1,count2,count3,count4;//四个年龄段
      |                                     ^~~~~~
foo.c:19:34: warning: 'count3' may be used uninitialized [-Wmaybe-uninitialized]
   19 |         printf("%.2lf%%\n",count3/n*100);
      |                            ~~~~~~^~
foo.c:9:30: note: 'count3' was declared here
    9 |         double count1,count2,count3,count4;//四个年龄段
      |                              ^~~~~~
foo.c:18:34: warning: 'count2' may be used uninitialized [-Wmaybe-uninitialized]
   18 |         printf("%.2lf%%\n",count2/n*100);
      |                            ~~~~~~^~
foo.c:9:23: note: 'count2' was declared here
    9 |         double count1,count2,count3,count4;//四个年龄段
      |                       ^~~~~~
foo.c:17:34: warning: 'count1' may be used uninitialized [-Wmaybe-uninitialized]
   17 |         printf("%.2lf%%\n",count1/n*100);
      |                            ~~~~~~^~
foo.c:9:16: note: 'count1' was declared here
    9 |         double count1,count2,count3,count4;//四个年龄段
      |                ^~~~~~

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