Introduction to Programming

Transcription

1 Introduction to Programming Summer Term 2014 Dr. Adrian Kacso, Univ. Siegen Tel.: 0271/ , Office: H-B 8406 State: April 9, 2014 Betriebssysteme / verteilte Systeme Introduction to Programming (1) i

2 Introduction to Programming Summer Term Introduction Betriebssysteme / verteilte Systeme Introduction to Programming (1) 16

3 1 Introduction... Contents Algorithms and programs The first C++ program Betriebssysteme / verteilte Systeme Introduction to Programming (1) 17

4 1.1 Algorithms and programs From Problem... to Solution Problem Creativity Intuition Mental Exercise Programming Solution Idea Algorithm Program Automatic (Compiler, OS, CPU) (Automatic) Execution Betriebssysteme / verteilte Systeme Introduction to Programming (1) 18

5 1.1 Algorithms and programs... Algorithms An algorithm: Or: is a set of instructions with a precise statement ( meaning) of effective ( actually executable) processing steps noted in a precisely defined language An algorithm is a prescription how to solve a problem using individual, small steps Betriebssysteme / verteilte Systeme Introduction to Programming (1) 19

6 1.1 Algorithms and programs... Algorithms An algorithm: Or: is a set of instructions with a precise statement ( meaning) of effective ( actually executable) processing steps noted in a precisely defined language An algorithm is a prescription how to solve a problem using individual, small steps Betriebssysteme / verteilte Systeme Introduction to Programming (1) 19

7 1.1 Algorithms and programs... Pizza algorithm 1. Get the incredients (flour, salt, eggs, sugar, vegetables...) 2. First clean the flour with a sieve 3. Then add 1 cup of flour, 1 tsp yeast, 1 tsp sugar, 1/2 cup warm water, 2 tablespoons of olive oil, 1 tsp salt. Mix the yeast, sugar and water and make sure it bubbles up 4. Meanwhile wash the tomatos, cut the salami, Then mix with all the other ingredients until combined and then knead the dough for about 10 minutes. Let the dough rise. 6. spread salami, tomato over the pizza and then top with cheese 7. If using circulating oven, bake at 180 C for 20 minutes Otherwise, heat oven to 210 C... Betriebssysteme / verteilte Systeme Introduction to Programming (1) 20

8 1.1 Algorithms and programs... The Computer from inside (VERY simplistic) registers registers memory bus CPU ALU disk Betriebssysteme / verteilte Systeme Introduction to Programming (1) 21

9 1.1 Algorithms and programs... How the CPU works Both binary program and data are in the memory (a sequence of cells, e.g., bytes) Execution: load operation from memory cell addressed by PC to CPU execute the operation increment the PC (PC = Program Counter) Operation can be: load contents of a memory cell to a register perform operation (in the ALU) between registers store a register s contents to a memory cell change the PC Betriebssysteme / verteilte Systeme Introduction to Programming (1) 22

10 1.1 Algorithms and programs... From problem... to solution problem thinking algorithm programming program (C++) compiler solution! CPU binary program One hour of thinking can easily save one week of programming! Or: programming is not trial-and-error! Betriebssysteme / verteilte Systeme Introduction to Programming (1) 23

11 1.2 The First C++ Program The C++ Programming Language developed by B. Stroustrup (in 1983) as an extension of C. Imperative prescribes exactly which statements have to be executed in which order. Object-oriented allows the use of objects and classes A program can be viewed as a collection of classes that are used to produce objects. C++ is in between problem description and CPU operation. (Many say that it is closer to the CPU... ) Betriebssysteme / verteilte Systeme Introduction to Programming (1) 24

12 1.2 The First C++ Program... The first C++ Program #include <iostream> using namespace std; int main() { cout << "Hello, world!\n"; return 0; } All (non-white-space) characters are important C++ is case sensitive: return Return homework: try this with the compiler Betriebssysteme / verteilte Systeme Introduction to Programming (1) 25

13 1.2 The First C++ Program... Parts of a Simple Program #include preprocessor directive (# pound symbol) includes the contents of another file using namespace where to search unknown names main() function starting point of the program Statements prescription what to do Comments: // comment which ends at the end of the line /* comment which may have multiple lines. It ends here: */ Betriebssysteme / verteilte Systeme Introduction to Programming (1) 26

14 1.2 The First C++ Program... The main() Function Conventional: tells the compiler where the program starts Is of type int (returns an integer number) Return value is given back to the operating system after the program has terminated (ended) The program executes the statements inside main(), exactly in the given order, from the beginning (top) to the end (bottom) Betriebssysteme / verteilte Systeme Introduction to Programming (1) 27

15 1.2 The First C++ Program... The first C++ Program / Author: James Bond Program: first.cpp Description: first program / #include <iostream> using namespace std; // iostream library // standard library namespace int main() { cout << "Hello, world!\n"; // Message // program s main function } return 0; // Program termination Betriebssysteme / verteilte Systeme Introduction to Programming (1) 28

16 1.2 The First C++ Program... Compiling a Program x.h header files (include files) init program init memory call main() return result x.cpp preprocess x.cpp compile x.o link hello source file source file object file executable On the lab computers: g++ x.cpp -o hello Betriebssysteme / verteilte Systeme Introduction to Programming (1) 29

17 1.2 The First C++ Program... Functions #include <iostream> using namespace std; int add(int x, int y) { // this is a function return (x+y); } int main() { int a,b,c; cout << "Enter two numbers: "; cin >> a; cin >> b; c = add(a,b); cout << "The sum is " << c << endl; return 0; } Betriebssysteme / verteilte Systeme Introduction to Programming (1) 30

18 1.2 The First C++ Program... Functions... Statements (e.g., in main()) are executed in their order in the code When a function is called, the program branches to the beginning of it A function consists of header and body header: type name ( parameter-list ) body: { list-of-statements } A function returns when it executes the return statement (or when it reaches the end of its body) Betriebssysteme / verteilte Systeme Introduction to Programming (1) 31

19 1.2 The First C++ Program... Remark on used notations Throughout the slides, the following styles are used: typewriter and typewriter for program text, text typed into the computer, text printed by the computer e.g., main(), ; green italics for non-terminal symbols: names standing for parts of a program (or a command) e.g., parameter-list bold blue for terms being defined red and italics to emphasize text Betriebssysteme / verteilte Systeme Introduction to Programming (1) 32

20 1.2 The First C++ Program... Debug Output We can add more output to see what the program is doing: #include <iostream> using namespace std; int add(int x, int y) { cout << "In add(), received " << x << " and " << y << "\n"; return (x+y); } Betriebssysteme / verteilte Systeme Introduction to Programming (1) 33

21 1.2 The First C++ Program... Debug Output... int main() { cout << "I m in main()!\n"; int a,b,c; cout << "Enter two numbers: "; cin >> a; cin >> b; cout << "\ncalling add()\n"; c = add(a,b); cout << "\nback in main().\n"; cout << "The sum is " << c << endl; cout << "Exiting...\n\n"; return 0; } Betriebssysteme / verteilte Systeme Introduction to Programming (1) 34

22 1.3 Repetition The first C++ Program #include <iostream> using namespace std; int main() { cout << "Hello, world!\n"; Insert a file with definitions for input/output Search names in the name space std Main function: the execution will start here A statement: print a text } return 0; Another statement: return from the function Betriebssysteme / verteilte Systeme Introduction to Programming (1) 35

23 1.3 Repetition... From Problem... to Solution problem thinking algorithm programming program (C++) compiler solution! CPU binary program Betriebssysteme / verteilte Systeme Introduction to Programming (1) 36