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@ -1,12 +1,13 @@ |
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This post aims to cover all the major topics that C programmers need to know before |
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they start writing C++ programs. I kept this post as short and concise as possible to |
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enable people to use this as a quick reference to jump into C++. This post assumes |
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that you have prior knowledge of both C and object oriented programming concepts. |
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enable people to use this as a quick reference to quickly jump into C++. This post assumes |
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that you have prior knowledge of both C and object oriented-programming concepts. Each topic |
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is quickly covered in a code snippet and some additional explanation is provided if necessary. |
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## Input/Output |
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Input and output in C++ is pretty easy, you just use "cout" and "cin". When printing with |
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"cout", you separate what your printing with "<<", the "endl" at the end prints a new line. |
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Input and output in C++ is easy, you use "cout" and "cin". When printing with |
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"cout", you separate what your printing with "<<"; "endl" prints a new line. |
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```c++ |
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using namespace std; //namespaces talked about below |
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@ -17,7 +18,7 @@ int main() |
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cout << "Hello World" << endl; // HELLO WORLD! |
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int a; |
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cin >> a; //inputs an int into a |
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cin >> a; //inputs an int into a -- notice how arrows face the direction of IO |
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cout << "You entered: " << a << endl; //prints what you entered |
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@ -26,9 +27,9 @@ int main() |
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``` |
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If you wish to run a C++ program simply save it with the extension ".cpp", you then |
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Save your C++ programs with the extension ".cpp", you then |
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can compile and run it with g++. Compiling a C++ program with g++ is nearly the same |
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as compiling a C program with gcc. |
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as compiling a C program with GCC. |
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ex: |
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@ -42,8 +43,8 @@ g++ helloWorld.cpp -o hello |
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Name spaces are used to enable you to have multiple functions/methods called the |
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same thing and not conflict with one another. You use "namespacename::function/variable" |
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to access something inside of a namespace. To prevent you from always having to type |
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"namespacename::", you can use a namespace which makes that namespace "default". |
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to access something inside of a specific namespace. To prevent you from always having to type |
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"namespacename::", you can use a namespace which makes that namespace default. |
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```c++ |
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using namespace std; //tells compiler we want to use std namespace |
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@ -91,7 +92,7 @@ int main() |
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## Global Variable |
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Similar to C, however, you can now reference a global variable with the "::" |
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Global variables are similar to C, however, you can now reference a global members with the "::" |
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accessor. |
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```c++ |
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@ -113,7 +114,7 @@ int main () |
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## Multiple Names for a Variable/Aliasing |
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This is simply NOT a pointer. In the following example pi, and x now are treated as |
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This is NOT simply a pointer. In the following example pi, and x now are treated as |
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the same exact variable. You cannot later change the pointer destination for x. |
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@ -129,16 +130,15 @@ cout << "pi: " << pi << " x: " << x << endl; // prints pi: 2.1 x: 2.1 |
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## Passing Variables by Reference |
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In C, everything was passed by value -- only way to get around this was by passing |
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pointers. C++ now allows us to pass variables by reference. This is very powerful, in |
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In C, everything was passed by value; C++ allows us to pass variables by reference. This is very powerful, in |
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languages like Java, only Objects are passed by reference. C++ lets you decide exactly |
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what gets passed by reference or by value. |
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what gets passed by reference or by value -- even primitives. |
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```c++ |
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using namespace std; |
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#include <iostream> |
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void change (int &r, int s) //r is passed by reference |
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void change (int &r, int s) //& infront of variable means that it will get passed by reference |
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{ |
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r = 100; |
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s = 200; |
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@ -169,7 +169,7 @@ int main() |
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{ |
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int x = 1; |
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int y = 2; |
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printf("%d, %d", x, y); //printf doesn't exist in c++. |
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printf("%d, %d", x, y); |
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change(&x, y); |
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printf("%d, %d", x, y); |
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@ -178,9 +178,9 @@ int main() |
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``` |
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## Functions Returning Variables not Values |
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## Functions Returning Variables References |
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A function can return a variable -- not a value. In the following example, a function |
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A function can return a value reference which can be treated as a variable. In the following example, a function |
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returns the reference to the variable which is the smallest. |
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```c++ |
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@ -211,11 +211,11 @@ int main () |
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``` |
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## Inline -- similar to Macros |
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## Inline |
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Inline can be used to replace a function which contains very simple logic -- no |
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for loops, etc. Like a macro, this will be inserted everywhere the code is used; a |
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draw back to inline methods is that the compiled source will be larger. But, they |
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drawback to inline methods is that the compiled source will be larger. But, they |
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typically run faster. |
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```c++ |
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@ -240,7 +240,7 @@ int main() |
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## Exceptions |
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Exceptions might help you stop segmentation faulting. The important thing to notice |
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is that you can throw just about any type in a try block. |
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is that you can throw about any type in a try block. |
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```c++ |
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int x; |
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@ -269,7 +269,7 @@ This is exactly like default parameters in Python. If a function is called witho |
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the parameter, it is assumed to be that value. |
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```c++ |
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double multiply(double x, double y = 5) |
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double multiply(double x, double y = 5) // y has the default value of 5 |
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{ |
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return x * y; |
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} |
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@ -439,9 +439,9 @@ struct pair |
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The syntax of a class is similar to a struct. |
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```c++ |
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class Pair |
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class Pair |
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{ |
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public: |
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public: // encapsulation covered in 2 sections |
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int i; |
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int x; |
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@ -454,9 +454,9 @@ public: |
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## Class Constructor and De-constructor |
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Class constructors are similar to constructors in java. Class de-constructors |
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Class constructors are similar to constructors in Java. Class destructor |
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are simply the name of the class with a "~" sign in front of it. It is important to |
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free any allocated memory in the class deconstruct. |
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free any allocated memory in the class deconstruct since C++ does not have a garbage collector. |
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```c++ |
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class Pair |
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@ -558,9 +558,9 @@ private: |
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## Class Inheritance |
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Classes can inherit variables and methods from other classes. The major thing to |
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remember is that if you ever want to override a method in a child class, you have |
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to declare the method as "virtual". |
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Classes can inherit variables and methods from other classes. The most important thing to |
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remember is that if you ever want to override a method in a child class, you must |
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declare the method as "virtual". |
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```c++ |
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class Pair |
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@ -588,7 +588,7 @@ protected: |
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int z; |
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public: |
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Triple(int i1, int i2, int i3): Pair(i1, i2) //calls the parent classes constructor |
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Triple(int i1, int i2, int i3): Pair(i1, i2) //calls the parent's constructor |
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{ |
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z = i3; |
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} |
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}; |
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``` |
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## "Abstract" Classes |
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## Abstract Classes |
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Abstract classes are simply classes which can not be instantiated. To do this in C++ |
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Abstract classes are simply classes which cannot be instantiated. To do this in C++ |
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you simply set a virtual function equal to zero. |
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```c++ |
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@ -625,8 +625,8 @@ public: |
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## Method Prototypes for Classes |
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If you wish to have a method prototype in a class, you have to use namespace |
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syntax to define it elsewhere. This is particularly useful for breaking a class |
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If you wish to use a method prototype in a class, you must use namespace |
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syntax to define the method elsewhere. This is particularly useful for breaking classes |
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into multiple files. It is common to declare the class in a header file and then |
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implement the functions in a cpp file. |
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@ -657,7 +657,7 @@ int Cat::fly() |
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## Strings |
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Since C++ has classes, it can now work with strings in a more pleasant way. |
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Since C++ has classes, you can work with strings in a pleasant way. |
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```c++ |
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using namespace std; |
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@ -671,10 +671,10 @@ int main() |
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string str1Copy(str1); // string "Hello" |
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//initalizes string by a character and number of occurances |
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//initializes string by a character and number of occurrences |
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string str4(5, '$'); // string "$$$$$$" |
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//string contatination |
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//string concatenation |
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string greeting = str1 + " " + str2; |
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cout << greeting << endl; |
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//returns last character in string |
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char back = numbers.back(); |
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//gets character at a certain position |
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//gets a character at a certain position |
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char second = numbers.at(1); |
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char secondAlt = numbers[1]; |
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char secondAlt = numbers[1]; //array syntax still works on strings |
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cout << "first: " << first << endl; |
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cout << "back: " << back << endl; |
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//substr(a, b) function returns a substring of b length |
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//starting from index a. if there is no second argument, it |
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//starting from index a. If there is no second argument, it |
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//goes to the end. |
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cout << numbers.substr(2, 7) << endl; |
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# File IO |
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File IO is significantly different in C++. I will quickly glance over |
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a few examples which should give you most of what you need to start writing some programs. |
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File IO is significantly different from C. I will quickly glance over |
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a few examples which should give you most of what you need to start writing basic programs. |
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## Reading From File |
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## Reading from File |
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Reading a file example by character. |
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@ -733,7 +733,7 @@ Reading a file example by character. |
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using namespace std; |
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#include <iostream> |
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#include <fstream> // Header for files |
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#include <fstream> // header for files |
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int main() |
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{ |
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{ |
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string line; |
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ifstream myfile ("example.txt"); |
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if(myfile.is_open()) //checks to see if file open sucessfully |
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if(myfile.is_open()) //checks to see if file open successfully |
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{ |
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while(getline(myfile,line)) //gets contents of file and puts them in a string |
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{ |
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## Resources |
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You should now know enough C++ to start developing with it. If you want to take your C++ |
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You now know enough C++ to start programming with it. If you want to take your |
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skills to the next level, I would recommend start working on a few projects in C++ and get |
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a comprehensive C++ book. |
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- [Online C++ Guide](https://www.programiz.com/cpp-programming) |
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- Kochan: Programming in C _p4 (4th Edition) (Developer's Library) 4th Edition -- Really good book if you don't know C that good. |
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- Kochan: Programming in C _p4 (4th Edition) (Developer's Library) 4th Edition -- Really good book if you don't know C yet. |
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- [Tutorials Point C++](https://www.tutorialspoint.com/cplusplus/index.htm) |
jrtechs
7 years ago