The 10 Most Common C++ Mistakes

The 10 Most Common C++ Mistakes

Although many C++ programmers take measures to prevent bugs, mistakes still slip through. This list of the ten most common mistakes while writing C++ code can help both new and veteran programmers:

    You forgot to declare the variable.

    You used the wrong uppercase and lowercase letters; for example, you typed Main when you meant main.

    You used one equal sign (=) when you were supposed to use two (==), either in an if statement or in a for loop.

    You forgot #include <iostream> or using namespace std;.

    You dropped the laptop in the swimming pool.

    You forgot to call new and just started using the pointer anyway.

    You forgot the word public: in your classes so everything turned up private.

    You let the dog eat the remote.

    You forgot to type the parentheses when calling a function that takes no parameters.

    You forgot a semicolon, probably at the end of a class declaration.

The Usual C++ Header Files

In C++, a header file holds forward declarations of identifiers. Here are some of the most common C++ header files that you’ll be using, along with their correct spellings. These aren’t by any means all of them, but they are the most common:

    Include <string> if you’re going to be using the string class.

    Include <iostream> when you want to use cout and cin.

    Include <fstream> when you want to read or write files.

    Include <iomanip> if you want advanced manipulator usage in your streams.

    Include <stdlib.h> for general operations, including system(“PAUSE”).

C++ Syntax that You May Have Forgotten

Remembering a bunch of C++ syntax can make you “loopy.” The following samples show the syntax of some of the more easily forgotten C++ situations: a for loop, a while loop, and a switch statement; a class and the code for a member function; a base class and a derived class; a function, function pointer type, and pointer to the function; and a class template and then a class based on the template.


// Here’s a for loop:

int i;
for (i=0; i<10; i++) {
    cout << i << endl;
}

// Here’s a while loop that counts from 10 down to 1:

int i = 10;
while (i > 0) {
    cout << i << endl;
    i—;
}

// And here’s a switch statement:

switch (x) {
case 1:
    cout << “1” < < endl;
case 2:
    cout << “2” << endl;
default:
    cout << “Something else” << endl;
}

// Here’s a class and the code for a member function:

class MyClass {
private:
    int x;
public:
    void MyFunction(int y);
};
void MyClass::MyFunction(int y) {
    x = y;
}

// Here’s a base class and a derived class:

class MyBase {
private:
   // derived classes can
   // not access this
   int a;
protected:
   // derived classes can
   // access this
   int b;
};
class Derived : public MyBase {
public:
    void test() {
        b = 10;
    }
};

// Here’s a function, a function pointer type, and a pointer to the function:

int function(char x) {
    return (int)x;
}
typedef int (* funcptr)(char);
funcptr MyPtr = function;

// And here’s a class template and then a class based on the template:

template <typename T>
class MyTemplate {
public:
    T a;
};
MyTemplate<int> X;