當你寫一份宣告，根據C ++語言的語法無效時發生語法錯誤。這包括錯誤，如缺少分號，未宣告的變數，不匹配的括號或大括號，和未終止字串。例如，下面的程式中包含相當多的語法錯誤：

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#include <iostream>; // preprocessor statements can't have a semicolon on the end
 
int main()
{
    std:cout < "Hi there; << x; // invalid operator (:), unterminated string (missing "), and undeclared variable
    return 0 // missing semicolon at end of statement
}
 

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#include <iostream>
 
int main()
{
    int a = 10;
    int b = 0;
    std::cout << a << " / " << b << " = " << a / b; // division by 0 is undefined
    return 0;
}