C++ : The #include iostream exists, but I get an error: identifier 'cout' is undefined. Why?

C++ : The #include iostream exists, but I get an error: identifier "cout" is undefined. Why?
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C++ : The #include iostream exists, but I get an error: identifier "cout" is undefined. Why?
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iostream is exists, Why? #include get C++ but I : "cout" an The identifier error: undefined.