Variables and Data Types.pdf

Variables and Data Types Course Code: CC 123 (B) Course Title: Introduction to Programming (C++) Prepared by: Alvin Herrera, Instructor 1 Variables. Data Types. The usefulness of the "Hello World" programs shown in the previous section is quite questionable. We...

Variables and Data Types Course Code: CC 123 (B) Course Title: Introduction to Programming (C++) Prepared by: Alvin Herrera, Instructor 1 Variables. Data Types. The usefulness of the "Hello World" programs shown in the previous section is quite questionable. We had to write several lines of code, compile them, and then execute the resulting program just to obtain a simple sentence written on the screen as result. It certainly would have been much faster to type the output sentence by ourselves. However, programming is not limited only to printing simple texts on the screen. In order to go a little further on and to become able to write programs that perform useful tasks that really save us work we need to introduce the concept of variable. Variables. Data Types. Let us think that I ask you to retain the number 5 in your mental memory, and then I ask you to memorize also the number 2 at the same time. You have just stored two different values in your memory. Now, if I ask you to add 1 to the first number I said, you should be retaining the numbers 6 (that is 5+1) and 2 in your memory. Values that we could now for example subtract and obtain 4 as result. Variables. Data Types. The whole process that you have just done with your mental memory is a simile of what a computer can do with two variables. The same process can be expressed in C++ with the following instruction set: a = 5; b = 2; a = a + 1; result = a - b; Variables. Data Types. Obviously, this is a very simple example since we have only used two small integer values, but consider that your computer can store millions of numbers like these at the same time and conduct sophisticated mathematical operations with them. Therefore, we can define a variable as a portion of memory to store a determined value. Each variable needs an identifier that distinguishes it from the others, for example, in the previous code the variable identifiers were a, b and result, but we could have called the variables any names we wanted to invent, as long as they were valid identifiers. Identifiers A valid identifier is a sequence of one or more letters, digits or underscore characters (_). Neither spaces nor punctuation marks or symbols can be part of an identifier. Only letters, digits and single underscore characters are valid. In addition, variable identifiers always have to begin with a letter. They can also begin with an underline character (_ ), but in some cases these may be reserved for compiler specific keywords or external identifiers, as well as identifiers containing two successive underscore characters anywhere. In no case they can begin with a digit. Identifiers Another rule that you have to consider when inventing your own identifiers is that they cannot match any keyword of the C++ language nor your compiler's specific ones, which are reserved keywords. The standard reserved keywords are: asm, auto, bool, break, case, catch, char, class, const, const_cast, continue, default, delete, do, double, dynamic_cast, else, enum, explicit, export, extern, false, float, for, friend, goto, if, inline, int, long, mutable, namespace, new, operator, private, protected, public, register, reinterpret_cast, return, short, signed, sizeof, static, static_cast, struct, switch, template, this, throw, true, try, typedef, typeid, typename, union, unsigned, using, virtual, void, volatile, wchar_t, while Identifiers Additionally, alternative representations for some operators cannot be used as identifiers since they are reserved words under some circumstances: and, and_eq, bitand, bitor, compl, not, not_eq, or, or_eq, xor, xor_eq Your compiler may also include some additional specific reserved keywords. Identifiers Very important: The C++ language is a "case sensitive" language. That means that an identifier written in capital letters is not equivalent to another one with the same name but written in small letters. Thus, for example, the RESULT variable is not the same as the result variable or the Result variable. These are three different variable identifiers. Naming Conventions C++ has a set of rules for naming variables, functions, and other identifiers in your code. These rules, known as naming conventions, help to make your code more readable and maintainable. Guidelines for Naming Conventions in C++ Variable names should be descriptive and meaningful. For example, a variable that holds the number of students in a class could be named "numStudents" or "studentCount". Variable names should be in lowercase, with words separated by underscores. For example, "student_count" or "total_income". Functions should be named using camelCase, with the first letter of each word in uppercase except for the first word. For example, "calculateTotalIncome" or "getStudentCount". Guidelines for Naming Conventions in C++ Constants should be named in uppercase, with words separated by underscores. For example, "PI" or "MAX_STUDENT_COUNT". Class names should be in CamelCase, with the first letter of each word in uppercase except for the first word. For example, "Student" or "CourseEnrollment". Avoid using abbreviations or acronyms that might not be familiar to other programmers. Avoid using reserved words or keywords as variable or function names. Advantages of Naming Conventions Improved readability: ○ Using a consistent naming convention can make it easier to understand the purpose of a variable or function by looking at its name. For example, if you consistently use camelCase for variables and PascalCase for functions, it will be clear at a glance which are variables and which are functions. Enhanced Maintainability: ○ Consistent naming conventions can help you locate specific variables or functions in your code more easily. For example, suppose you consistently use a specific prefix or suffix for variables that store certain types of data (such as "str" for strings or "arr" for arrays). In that case, it will be easier to find all variables of that type when you need to make changes. Advantages of Naming Conventions Reduced Errors: ○ Using a consistent naming convention can help reduce errors in your code by making it easier to identify variables or functions that have similar names but serve different purposes. For example, suppose you consistently use a specific prefix or suffix for variables that store certain types of data (such as "str" for strings or "arr" for arrays). In that case, it will be easier to catch errors caused by using the wrong type of variable in a given context. Increased Collaboration: ○ A consistent naming convention can make it easier for multiple people to work on the same codebase, as it helps to ensure that everyone is using the same naming conventions. This can help avoid confusion and reduce the risk of conflicts when merging code changes. Advantages of Naming Conventions Enhanced Professionalism: ○ Adhering to a consistent naming convention demonstrates professionalism and attention to detail, which can be especially important when working on projects with clients or in a professional setting. Using a consistent naming convention can also make your code more visually appealing and easier to read, which can be a valuable asset in any situation. Disadvantages of Naming Conventions Extra effort: ○ Adhering to a consistent naming convention requires extra effort and discipline, as you have to remember to use the correct conventions every time you name a variable or function. This can be especially challenging if you are working with a team that has different naming conventions, or if you are working on a project that requires you to follow a specific naming convention that is different from what you are used to. Limitations: ○ Using a consistent naming convention can also be limiting, as it may restrict the names you can use for variables or functions. For example, if you are using a naming convention that requires you to use a specific prefix or suffix for certain types of variables, you may not be able to use certain names that you would otherwise prefer. Disadvantages of Naming Conventions Potential for conflict: ○ Different people or teams may have different preferences when it comes to naming conventions, which can lead to conflicts if everyone is not on the same page. This can be especially problematic if you are working on a large project with many contributors. Lack of flexibility: ○ Depending on the naming convention you are using, it may not always be the most appropriate or intuitive choice for every situation. For example, if you are using a convention that requires you to use camelCase for variables, you may have to come up with less intuitive names for variables that would be more naturally expressed using underscores or other separators. Fundamental Data Types When programming, we store the variables in our computer's memory, but the computer has to know what kind of data we want to store in them, since it is not going to occupy the same amount of memory to store a simple number than to store a single letter or a large number, and they are not going to be interpreted the same way. The memory in our computers is organized in bytes. A byte is the minimum amount of memory that we can manage in C++. A byte can store a relatively small amount of data: one single character or a small integer (generally an integer between 0 and 255). In addition, the computer can manipulate more complex data types that come from grouping several bytes, such as long numbers or non-integer numbers. Fundamental Data Types Name Description Size Range True or false boolean Store true or false values 1 byte Store a single character/letter/number char 1 byte -128 to 127 or ASCII values Store whole numbers, without -2, 147, 483, 648 to int 2 or 4 bytes decimals 2, 147, 483, 647 Stores fractional numbers, containing -3.4 × 10^38 to float one or more decimals. Sufficient for 4 bytes 3.4 × 10^38 storing 6-7 decimal digits Stores fractional numbers, containing -1.7 × 10^308 to double one or more decimals. Sufficient for 8 bytes 1.7 × 10^308 storing 15 decimal digits Declaration of Variables In order to use a variable in C++, we must first declare it specifying which data type we want it to be. The syntax to declare a new variable is to write the specifier of the desired data type (like int, bool, float...) followed by a valid variable identifier. For example: int a; float mynumber; These are two valid declarations of variables. The first one declares a variable of type int with the identifier a. The second one declares a variable of type float with the identifier mynumber. Once declared, the variables a and mynumber can be used within the rest of their scope in the program. Declaration of Variables If you are going to declare more than one variable of the same type, you can declare all of them in a single statement by separating their identifiers with commas. For example: int a, b, c; This declares three variables (a, b and c), all of them of type int, and has exactly the same meaning as: int a; int b; int c; Sample program // operating with variables // process: #include a = 5; using namespace std; b = 2; int main () { a = a + 1; // declaring variables: result = a - b; int a, b; // print out the result: int result; cout