foo.c: In function 'main':
foo.c:18:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&num);
     ^~~~~~~~~~~~~~~~
foo.c: In function 'huiwen':
foo.c:12:16: warning: 'sum' may be used uninitialized in this function [-Wmaybe-uninitialized]
     return (sum==nn);
            ~~~~^~~~~
foo.c: In function 'main':
foo.c:19:7: warning: 'sum' may be used uninitialized in this function [-Wmaybe-uninitialized]
     if(huiwen(num))
       ^

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