foo.cc: In function 'int main()':
foo.cc:6:11: warning: right operand of comma operator has no effect [-Wunused-value]
  cin>>a,b,c,x;
           ^
foo.cc:6:13: warning: right operand of comma operator has no effect [-Wunused-value]
  cin>>a,b,c,x;
             ^
foo.cc:6:14: warning: right operand of comma operator has no effect [-Wunused-value]
  cin>>a,b,c,x;
              ^
foo.cc:7:8: warning: 'b' is used uninitialized in this function [-Wuninitialized]
  x=20-a-b-c;  
    ~~~~^~
foo.cc:7:3: warning: 'c' is used uninitialized in this function [-Wuninitialized]
  x=20-a-b-c;  
  ~^~~~~~~~~

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