foo.cc: In function 'int main()':
foo.cc:5:20: error: 'a' was not declared in this scope
    5 |     scanf("%s %s",&a,&b);
      |                    ^
foo.cc:5:23: error: 'b' was not declared in this scope
    5 |     scanf("%s %s",&a,&b);
      |                       ^

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