CSE 1341 Honors Note Set 2 1

Overview  Java vs. C++  Functions in C++  First Programming Packet  Development Environment 2

Review 3

Main Function  Free floating main function in C++.  Doesn’t have to be inside a class public class JavaProgram { public static void main(String [] args) { System.out.println(“Hello World!”); } int main() { cout << “Hello World!”; } 4

Compiling  java compiles to bytecode that is later interpreted by the JVM  Should theoretically be able to transfer even compiled code to a different machine – Platform Independence  C++ compiles to machine code that is directly executable on the machine  Compiled code will only run on one OS/Machine type  Executable is not necessarily universally portable 5

Syntax Formatting  No real major difference – More of coding conventions to deal with  Where do we put braces?  Usually on the next line  Does it really matter?  No int main() { for (int j = 0; j < 10; j++) { cout << “Hello World!” << endl; } 6

Using Libraries 7  What’s this #include stuff??  #include  Anything with a # is handled by the C++ Preprocessor  iostream is a library of io functionality  there is actually a file in the file system named iostream  the contents of the iostream file are effectively copied into the place of the #include  other things can appear between the <> such as fstream, iomanip, etc.  similar to an import in Java  using namespace std;  everything that is in the iostream file is part of the std namespace  Namespaces allow grouping of entities like classes, objects and functions using one name  Allows global scope to be subdivided, with each subdivision having its own name

Functions 8

9 int myfunction (int x, int y) { int sum = 0; for (int j = x; j < y; j++) sum += j; return sum; } int main() { int sum = myfunction(5, 10); cout << sum << endl; return 0; } arguments parameters

Pass By Value 10 int myfunction (int x, int y) { x = 60; y = 600; return x + y; } int main() { int a = 5, b = 10; int sum = myfunction(a, b); cout << a << “ “ << b << endl; return 0; } 5 10 a b 5 x y x and y have copies of a and b changing x or y does not affect a or b

Pass By Reference - & 11 int myfunction (int& x, int& y) { x = 60; y = 600; return x + y; } int main() { int a = 5, b = 10; int sum = myfunction(a, b); cout << a << “ “ << b << endl; return 0; } 5 10 a b x y x and y refer back to their arguments, a and b changing x or y DOES affect a or b

Pass By Reference - & 12 int myfunction (int& x, int& y) { x = 60; y = 600; return x + y; } int main() { int a = 5, b = 10; int sum = myfunction(a, b); cout << a << “ “ << b << endl; return 0; } a b x y x and y refer back to their arguments, a and b changing x or y DOES affect a or b

Pass By Reference - & 13 int myfunction (int& x, int& y) { x = 60; y = 600; return x + y; } int main() { int a = 5, b = 10; int sum = myfunction(a, b); cout << a << “ “ << b << endl; return 0; } a b x y x and y refer back to their arguments, a and b changing x or y DOES affect a or b What would main display?

Function Prototype 14 int myfunction(int&, int&); int main() { int a = 5, b = 10; int sum = myfunction(a, b); cout << a << “ “ << b << endl; return 0; } int myfunction (int& x, int& y) { x = 60; y = 600; return x + y; } Before a function can be called, the compiler must be told about its legal format Function definition can be placed before the call, or we can use a prototype Function Prototype allows the compiler to determine if a function call is legal Sort-of like a function declaration (like a variable declaration) Prototype

15 Default Function Arguments Default Arguments are arguments that are passed to parameters automatically if no argument is provided in the function call void displayStars(int = 10, int = 1);

16 Default Arguments void displayStars(int=10, int=1); int main() { displayStars(); displayStars(5); displayStars(7,3); return 0; } void displayStars(int cols, int rows) { for (int down=0; down<rows; down++) { for (int across=0; across<cols; across++) cout << “*”; cout << endl; }

17 Default Arguments void displayStars(int=10, int=1); int main() { displayStars(); displayStars(5); displayStars(7,3); return 0; } void displayStars(int cols, int rows) { for (int down=0; down<rows; down++) { for (int across=0; across<cols; across++) cout << “*”; cout << endl; }

18 Default Arguments void displayStars(int=10, int=1); int main() { displayStars(); displayStars(5); displayStars(7,3); return 0; } void displayStars(int cols, int rows) { for (int down=0; down<rows; down++) { for (int across=0; across<cols; across++) cout << “*”; cout << endl; }

19 Default Function Arguments  Rule  When an argument is left out of a function call, all arguments that come after it must also be left out. displayStars(,3)//Illegal someFunc(1,,3)//Illegal

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