First Program » Common Problems

It is worth paying attention to what can cause a compilation error. Compilation errors are caused by invalid C++. When the compiler encounters invalid code, it will stop and tell you what's wrong. You cannot run your program unless compilation is completed without errors.

Forgetting about std:: prefix

An error is caused if you omit std:: without the appropriate using statement.

🔴 Error message

GCC

error: ‘cout’ was not declared in this scope; did you mean ‘std::cout’?

🖼 Illustration of the error:

MSVC

error C2065: 'cout': undeclared identifier

🖼 Illustration of the error:

👌 Solution

Add using std::cout; to the top of your main function:

#include <iostream>
int main() {
	using std::cout;
	cout << "Hello, World!";
}

Forgotten includes

It's very easy to forget an #include, even for experts.

🔴 Error message

GCC

error: ‘cout’ is not a member of ‘std’

🖼 Illustration of the error:

MSVC

error C2039: 'cout': is not a member of 'std'
predefined C++ types (compiler internal)(341): note: see declaration of 'std'
error C2065: 'cout': undeclared identifier

🖼 Illustration of the error:

Missing semicolons ;

Beginners often forget the semicolons (;) at the end of statements. Study the code examples provided in this lesson carefully, paying attention to where they should go.

🔴 Error message

GCC

error: expected `;` before (...)

🖼 Illustration of the error:

MSVC

error C2143: syntax error: missing ';' before 'std::cout'

🖼 Illustration of the error:

Flaky Error Messages

Compilers have to guess where you missed a semicolon. Therefore if you are sure that you didn't miss a semicolon on the line it tells you about, try looking up a few lines.

Additionally missing semicolons can also cause unrelated errors further down your code. Usually the first error message given by the compiler is the most helpful one.

Unterminated text

Text is always between the quote characters "TEXT IS HERE!". Forgetting to add the second quotation mark leads to compiler thinking the rest of your program is text causing numerous errors.

🔴 Error message

GCC

error: missing terminating " character

🖼 Illustration of the error:

MSVC

error C2001: newline in constant
error C2143: syntax error: missing ';' before '}'

🖼 Illustration of the error:

Using " inside of text

You may be tempted to put quotes inside a message when outputting it to the console. However, remember that C++ considers everything inside of "..." quotes to be text.

Thus, if you write:

"Hi! My name is "Slim Shady". Nice to meet you!"

C++ will interpret this as:

"TEXT" C++ CODE "TEXT"

🔴 Error message

GCC

error: unable to find string literal operator ‘operator""Slim’ with ‘const char [16]’, ‘long unsigned int’ arguments

🖼 Illustration of the error:

TODO

MSVC

error C3688: invalid literal suffix 'Slim'; literal operator or literal operator template 'operator ""Slim' not found
error C2146: syntax error: missing ';' before identifier 'Shady'
error C2065: 'Shady': undeclared identifier
error C2143: syntax error: missing ';' before 'string'

🖼 Illustration of the error:

Unhelpful errors

These error messages aren't that helpful! Your hint should be the fact that it is treating what you intend to be text as code.

👌 Solution

You can prevent this by using the \ backslash character to escape the quote.

"Hi! My name is \"Slim Shady\". Nice to meet you!"

Escape sequence

The \" is an example of an escape sequence. It tells the compiler to treat the next character as text.

We can also use the backslash to escape other characters, such as the backslash itself. As a result, we'll need to use two backslashes to get one in the output.

Code

std::cout << "C:\\Users\\SlimShady\\Desktop";

Console

C:\Users\SlimShady\Desktop