C Program Structure and tools

1. C++ Program Structure (and tools) Today we�ll talk generally about C++ development (plus a few platform specifics) We�ll develop, submit, and grade code in Windows It�s also helpful to become familiar with Linux E.g., on shell.cec.wustl.edu For example, running code through two different compilers can catch a lot more �easy to make� errors

2. Writing a C++ Program

3. What Goes Into a C++ Program? Declarations: data types, function signatures, classes Allows the compiler to check for type safety, correct syntax Usually kept in �header� (.h) files Included as needed by other files (to keep compiler happy) class Simple { typedef unsigned int UINT32; public: Simple (int i); int usage (char * program_name); void print_i (); private: struct Point2D { int i_; double x_; }; double y_; }; Definitions: static variable initialization, function implementation The part that turns into an executable program Usually kept in �source� (.cpp) files void Simple::print_i () { cout << �i_ is � << i_ << endl; } Directives: tell compiler (or precompiler) to do something More on this later

4. A Very Simple C++ Program #include <iostream> // precompiler directive using namespace std; // compiler directive // definition of function named �main� int main (int, char *[]) { cout << �hello, world!� << endl; return 0; }

5. What is #include <iostream> ? #include tells the precompiler to include a file Usually, we include header files Contain declarations of structs, classes, functions Sometimes we include template definitions Varies from compiler to compiler Advanced topic we�ll cover later in the semester <iostream> is the C++ label for a standard header file for input and output streams

6. What is using namespace std; ? The using directive tells the compiler to include code from libraries that have separate namespaces Similar idea to �packages� in other languages C++ provides a namespace for its standard library Called the �standard namespace� (written as std) cout, cin, and cerr standard iostreams, and much more Namespaces reduce collisions between symbols Rely on the :: scoping operator to match symbols to them If another library with namespace mylib defined cout we could say std::cout vs. mylib::cout Can also apply using more selectively: E.g., just using std::cout

7. What is int main (int, char*[]) { ... } ? Defines the main function of any C++ program Who calls main? The runtime environment, specifically a function often called something like crt0 or crtexe What about the stuff in parentheses? A list of types of the input arguments to function main With the function name, makes up its signature Since this version of main ignores any inputs, we leave off names of the input variables, and only give their types What about the stuff in braces? It�s the body of function main, its definition

8. What�s cout << �hello, world!� << endl; ? Uses the standard output iostream, named cout For standard input, use cin For standard error, use cerr << is an operator for inserting into the stream A member operator of the ostream class Returns a reference to stream on which its called Can be applied repeatedly to references left-to-right �hello, world!� is a C-style string A 14-postion character array terminated by �\0� endl is an iostream manipulator Ends the line, by inserting end-of-line character(s) Also flushes the stream

9. What about return 0; ? The main function should return an integer By convention it should return 0 for success And a non-zero value to indicate failure The program should not exit any other way Letting an exception propagate uncaught Dividing by zero Dereferencing a null pointer Accessing memory not owned by the program Indexing an array �out of range� can do this Dereferencing a �stray� pointer can do this

10. A Slightly Bigger C++ Program #include <iostream> using namespace std; int main (int argc, char * argv[]) { for (int i = 0; i < argc; ++i) { cout << argv[i] << endl; } return 0; }

11. int argc, char * argv[] A way to affect the program�s behavior Carry parameters with which program was called Passed as parameters to main from crt0 Passed by value (we�ll discuss what that means) argc An integer with the number of parameters (>=1) argv An array of pointers to C-style character strings Its array-length is the value stored in argc The name of the program is kept in argv[0]

12. for (int i = 0; i < argc; ++i) Standard C++ for loop syntax Initialization statement done once at start of loop Test expression done before running each time Expression to increment after running each time int i = 0 Declares integer i (scope is the loop itself) Initializes i to hold value 0 (not an assignment!) i < argc Tests whether or not we�re still inside the array! Reading/writing memory we don�t own can crash the program (if we�re really lucky!) ++i increments the array position (why prefix?)

13. {cout << argv[i] << endl;} Body of the for loop I strongly prefer to use braces with for, if, while, etc., even w/ single-statement body Avoids maintenance errors when adding/modifying code Ensures semantics/indentation say same thing argv[i] An example of array indexing Specifies ith position from start of argv

14. Lifecycle of a C++ Program

15. Development Environment Studio We�ll follow a similar format most days in the course Around 30 minutes of lecture and discussion Then about 60 minutes of studio time Except for reviews before midterm/final, and midterm itself In the studios, please work in groups of 2 or 3 Exercises are posted on the course web page Record your answers to the exercises, and post to the course message board (as a reply to my message there) when you�re done We�ll migrate throughout the studio to answer questions Use studio time to develop skills and understanding A good chance to explore ideas you can use for the labs Exams will test understanding of the studio material You�re encouraged to try variations beyond the exercises