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Advantages and Disadvantages of Credit

Like most things, there are advantages and disadvantages to credit cards. Knowing some of these can help you decide if you do or do not want to use credit cards.

Advantages

• Purchase Power and Ease of Purchase - Credit cards can make it easier to buy things. If you don't like to carry large amounts of cash with you or if a company doesn't accept cash purchases (for example most airlines, hotels, and car rental agencies), putting purchases on a credit card can make buying things easier.
• Protection of Purchases - Credit cards may also offer you additional protection if something you have bought is lost, damaged, or stolen. Both your credit card statement (and the credit card company) can vouch for the fact that you have made a purchase if the original receipt is lost or stolen. In addition, some credit card companies offer insurance on large purchases.
• Building a Credit Line - Having a good credit history is often important, not only when applying for credit cards, but also when applying for things such as loans, rental applications, or even some jobs. Having a credit card and using it wisely (making payments on time and in full each month) will help you build a good credit history.
• Emergencies - Credit cards can also be useful in times of emergency. While you should avoid spending outside your budget (or money you don't have!), sometimes emergencies (such as your car breaking down or flood or fire) may lead to a large purchase (like the need for a rental car or a motel room for several nights.)
• Credit Card Benefits - In addition to the benefits listed above, some credit cards offer additional benefits, such as discounts from particular stores or companies, bonuses such as free airline miles or travel discounts, and special insurances (like travel or life insurance.) While most of these benefits are meant to encourage you to charge more money on your credit card (remember, credit card companies start making their money when you can't afford to pay off your charges!) the benefits are real and can be helpful as long as you remember your spending limits.

Disadvantages

• Blowing Your Budget -- The biggest disadvantage of credit cards is that they encourage people to spend money that they don't have. Most credit cards do not require you to pay off your balance each month, so even if you only have $100, you may be able to spend up to $500 or $1,000 on your credit card. While this may seem like 'free money' at the time, you will have to pay it off -- and the longer you wait, the more money you will owe since credit card companies charge you interest each month on the money you have borrowed.
• High Interest Rates and Increased Debt -- Credit card companies charge you an enormous amount of interest on each balance that you don't pay off at the end of each month. This is how they make their money and this is how most people in the United States get into debt (and even bankruptcy.) Consider this: If you have a $100 in savings, most banks will give you at the most 2.0 to 2.5% interest on your money over the course of the year. This means you earn $2.00 - $2.50 a year on your $100 savings. Most credit cards charge you up to 10 times that amount of interest on balances. This means that if you have $100 balance that you don't pay off, you will be charged 20-25% interest on that $100. This means that you owe almost $30 interest (plus the original $100) at the end of the year. A good way to look at this is in comparison to what you would earn in interest from a bank or owe in interest to a bank loan: Savings accounts may pay you around 2% interest; if you have a loan from a bank you may pay them around 10% interest (5 times as much as you earn off your savings); if you owe money to a credit card company, you may pay them around 20% interest (10 times as much as you earn off your savings.)
• Credit Card Fraud - Like cash, sometimes credit cards can be stolen. They may be physically stolen (if you lose your wallet) or someone may steal your credit card number (from a receipt, over the phone, or from a Web site) and use your card to rack up debts. The good news is that, unlike cash, if you realize your credit card or number has been stolen and you report it to your credit card company immediately, you will not be charged for any purchases that someone else has made. Even if you don't realize your credit card number has been stolen (sometimes you might not know until you receive your monthly statement), most credit card companies don't charge you or only charge a small fee, like $25 or $50, even if the thief has charged thousands of dollars to your card. There are several things you can do to prevent credit card fraud:
  • If you lose your card or wallet, report it to your credit card company immediately.
  • Don't loan your credit card to anyone and only give out your credit card information to trusted companies or Web sites.
  • Check your statement closely at the end of each month to make sure all charges are yours.
  • You can find out more about protecting your personal information by visiting our Personal Safety course.

Credit cards can make life easier and be a great tool, but if they aren't used wisely they can become a huge financial burden. If you do decide to use credit cards, remember these simple rules:

• Keep track of all your purchases.
• Don't spend outside your budget.
• Pay off your balance on all of your credit cards at the end of each month.
• Don't loan your credit or give out your credit card information to anyone but reliable companies.

Learn more about how to apply for credit cards in the next section

A declaration introduces a name – an identifier – to the compiler. It tells the compiler “This function or this variable exists somewhere, and here is what it should look like.” A definition, on the other hand, says: “Make this variable here” or “Make this function here.” It allocates storage for the name. This meaning works whether you’re talking about a variable or a function; in either case, at the point of definition the compiler allocates storage. For a variable, the compiler determines how big that variable is and causes space to be generated in memory to hold the data for that variable. For a function, the compiler generates code, which ends up occupying storage in memory. 

A definition can also be a declaration. If the compiler hasn’t seen the name xbefore and you define int x;, the compiler sees the name as a declaration and allocates storage for it all at once.

A function declaration in C and C++ gives the function name, the argument types passed to the function, and the return value of the function. For example, here is a declaration for a function called func1( ) that takes two integer arguments (integers are denoted in C/C++ with the keyword int) and returns an integer.

int func1(int, int);

A variable declaration tells the compiler what a variable looks like. It says, “I know you haven’t seen this name before, but I promise it exists someplace, and it’s a variable of X type.” 
In a function declaration, you give a type (the return value), the function name, the argument list, and a semicolon. That’s enough for the compiler to figure out that it’s a declaration and what the function should look like. By inference, a variable declaration might be a type followed by a name. For example:

int a;

could declare the variable a as an integer, using the logic above. Here’s the conflict: there is enough information in the code above for the compiler to create space for an integer called a, and that’s what happens. To resolve this dilemma, a keyword was necessary for C and C++ to say “This is only a declaration; it’s defined elsewhere.” The keyword is extern. It can mean the definition is external to the file, or that the definition occurs later in the file.

Declaring a variable without defining it means using the extern keyword before a description of the variable, like this:

extern int a;

Coming to your question, yes header files contains declarations but also some definitions. It mostly contains preprocessor directives like #define, #ifdef etc which the preprocessor step (before the compilation) will expand and allow functions and variables available for the compiling module.