foo.cc: In function 'int main()':
foo.cc:7:33: error: unable to find numeric literal operator 'operator""\U0000ff1b'
    7 |                 int sum=0,a=0,b=0；
      |                                 ^~~
foo.cc:7:33: note: use '-fext-numeric-literals' to enable more built-in suffixes
foo.cc:9:22: error: 'x' was not declared in this scope
    9 |                 cin>>x;
      |                      ^
foo.cc:7:21: warning: unused variable 'sum' [-Wunused-variable]
    7 |                 int sum=0,a=0,b=0；
      |                     ^~~

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