foo.cc: In function 'int main()':
foo.cc:7:7: error: 'wum' was not declared in this scope; did you mean 'sum'?
    7 | { sum=wum*10+i%10;
      |       ^~~
      |       sum
foo.cc:4:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
    4 |   scanf("%d",&i);
      |   ~~~~~^~~~~~~~~

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