Introduction to C++

1. Introduction to C++ Dr M.S. Colclough, research fellows, pgtas 5 weeks, 2 afternoons / week. Primarily a lab project. Approx. first 5 sessions start with lecture, followed by non-assessed exercises in lab. Later sessions devoted to a programming project (choose your own, or select from list). Assessment based on project. Hand-in dates as for lab: Phase 1: Fri 10 Dec 2010 (4pm) Phase 2: Fri 28 Jan 2011 (4pm) Labs equipped with Quincy editor and gcc Consult me if you wish to use your own system. Initial exercises are console (text) mode; graphical libraries later. Projects may or may not have graphical features. Teaching Support Office

2. Project Substantial, finished individual program High quality code: easy for others to understand / maintain / extend: clear logic, naming, data structures. Display sophistication in programming techniques: e.g. appropriate classes, use of external libraries, graphical interface, good algorithms. Good quality user interface: usable by others It's impossible to learn these skills in advance. Credit for acquiring these skills. Write a 1-2 page informal proposal for your project for approval by demonstrator. Does not have to be a physics calculation.

3. Resources Course web pages: www.cm.ph.bham.ac.uk/cpp Email: m.s.colclough@bham.ac.uk (Teach yourself/learn) (C++/Bengali) in (30 Days/21 Days/24 Hours/10 Minutes) - all exist! See the web pages for references to web sites and books, including several good free online ones e.g. Thinking in C++ Eckel Numerical recipes in C Press An introduction to C++ Chivers C++: A dialog Steve Heller If you don't already know C, avoid books that (i) assume you do, or (ii) teach C before C++. OK at this level: Programming with C++ Hubbard (Schaum's) C++ By Example Donovan (beware misprints) Accelerated C++ Koenig & Moo (intensive) Reference handbook: C/C++ Programmer's Reference Schildt

4. About C++ C was developed closely with the UNIX operating system (~1973) Mostly deals with ‘low-level’ data bytes, integers, floating point numbers, addresses (memory locations) Higher level than machine code (but not much) C++ was invented to make writing large scale software projects easier (~1983) the name C++ is an in-joke (++ in C/C++ = ‘the next one’) It is an ‘object oriented’ language can define high-level objects Originally conceived as ‘C with objects’ but the feature set expanded rapidly ISO standard finalised ~1998 We will only cover some of the most common and important features Using gcc/mingw 3.2 About Me: Steve Hillier (S.J.Hillier@bham.ac.uk)

5. Hello World #include <iostream> using namespace std; int main() { cout << "Hello World" << endl; } main is our first example of a function main is a very special function that the operating system calls when you start executing a program all programs must have a main no arguments – followed by () {}surround instructions to be performed Instructions consist of a number of statements followed by a semi-colon (one in this case) cout refers to the standard output stream (screen) endl jumps output to the next line << means ‘insert right-hand thing into left-hand thing’ #include <iostream> provides definition of cout, endl (called header file)

6. Streams and spacing There are several ways to do the same thing: #include <iostream> using namespace std; cout << "Last " << "night " << "I " << "dreamt"; cout << "Last "; cout << "night "; cout << "I "; cout << "dreamt"; cout << "Last night I dreamt"; Also spacing is (usually) unimportant for the compiler (‘whitespace’ is equivalent): #include <iostream> using namespace std; int main(){cout<<"Hello World"<<endl;} This would work just as well, but isn’t nice to look at – hence formatting conventions

7. Comments There are two styles – C++ style preferred // marks a comment that extends to // the end of the line. This is the // usual C++ style cout << endl; // Can be used here too /* This style makes a C-style comment that extends over several lines until the closing */ Comments are highly recommended Obligatory in assessed work Level of detail can be difficult to judge Try to say what or why, not how, eg // Calculate Julian date from // calendar date using algorithm from // Press et al.: Numerical Recipes

8. Strings First example of a data type. Declares a variable to contain characters and words As with streams, needs a header file: #include <string> // To create an empty string "" string firstName; // To create one with contents string secondName("Hillier"); // String of 25 question marks string bigQuery(25,’?’); firstName = "Steve"; // Change it // Join strings together... name = firstName + " " + secondName; // Read in from keyboard... cin >> name; // >> = extract lhs to rhs cout << name; Name.size(); // function returning length Strings have many other functions and operations

9. Variables and their names Just introduced the idea of a variable Declared to name an object that the program uses Declaration obligatory Can be of many types (including user defined) Variables can be changed Variable Names Initial letter + letters and digits: any length underscore is a letter: oh_yes_it_is case sensitive ie me, Me, mE, ME all different function names follow same rules several conventions used for names eg ALLCAPS traditionally used for constants: PI, MU0, … Some guidance: Must avoid reserved words eg static, else, throw… Should be highlighted by editor Good choice of names helps to make your program clearer

10. More Variables - Numerical Computers are good at working with numbers, so not surprisingly there’s lots of language support // Integers (±2,000,000,000) int i; // Declare i as an integer or int i=25; // declare and assign value or int i(25); // C++ style declare and assign // single precision floating point // (1e38, 6 digit precision) float x, y, z; // Declare three at once // double precision (more common) // (1e308, 15 digit precision) double a, b, bigNumber; Exact limits depend on compiler/operating system. These are typical values. Basic arithmetic operations are built into language int total; // assign new value as result of expression total = i + j*k +p/q;

11. Expressions In arithmetical expressions, the usual precedence rules apply (* before + etc). Expressions involving mixed types invoke type promotion (int to float to double). Integer division ignores remainder 3/4 = 0 (integer division) 3.0/4 = 0.75 (float division) double s, u, t, a; s = u*t + 0.5*a*t*t; There are some new operators: int i(7); int j(4); int remainder = i%j; // result is 3; i += 5; // Is equivalent to... i = i+5; // so i is now 17 j = i++; // now j is 17 (old i), i is 18 j = ++i; // now j is 19 (new i), i is 19 i++; // increment i, now 20 i--; // decrement I, now 19 again

12. Choices, choices… if A program can’t be very intelligent if it always Executes the same instructions. Therefore need choices and program control Probably the simplest is the if...else construct if ( cash > 50 ) { party; party; } else { work; } Note on structure blocks of code surrounded by {} else optional if condition in () Many other ‘comparison’ operators <, >, <=, >=, ==, != Take care with == (test for equality)

13. For loops Extremely powerful and flexible control structure. Used for repeating instructions (iteration). Typical loop: counts sums, and sum of squares of integers from 1 to 10. int sum(0); int sumSquares(0); for ( int i=1 ; i<=10 ; i++ ) { sum += i; sumSquares += i*i; } Syntax similar to if, but ‘condition’ consists of three parts: int i=1 // initialisation i<10 // condition, end loop if false i++ // perform at end of each loop In this case the loop counter, i, starts at 1, and the loop is performed for i = 1, 2, 3, … 9, 10. Initialisation, end action, can be more complex

14. Calling external functions For mathematical manipulations more complex than multiply, divide etc, need external functions. Many functions declared in <cmath> header. geometric – sin, cos, etc exponential – exp, ln others – pow, sqrt Examples: #include <cmath> double s, a, b, c; // pythagoras s = sqrt( pow(b,2) + pow(c,2) ); // triangle area area = pow(b,2) + pow(c,2) - 2*b*c*cos(a);

15. Formatting Output There are many formatting functions for cout. Used to ‘tidy up’ output. // 4 digit floating point numbers cout.precision(4); // 10 character space cout.width(10); // Fill blank characters with # cout.fill(‘#’); Shorthand for all above using ‘manipulators’: #include <iomanip> cout << setprecision(4); cout << setw(10); cout << setfill(‘#’); Note width setting is for next item only: cout << setw(10) << 3.2; Many other options (scientific notation, justification)