University:
Boston University
Course:
MET CS 201 | Introduction to Programming
Academic year:

2024
Views:

289

Pages:

15
Author:

Dinllugwyu6k3

Behind the Scenes: The Compilation Process Hello, World! explained The main routine – the start of every C++ program! It returns an integer value to the operating system and takes no arguments (). Statement that returns an integer value to the operating system after completion. 0 means “no error” Hello, World! explained loads a header file containing function and class definitions Loads a namespace called std. Namespaces are used to separate sections of code for programmer convenience. To save typing we’ll always use this line in this tutorial. cout is the object that writes to the stdout device, i.e. the console window. It is part of the C++ standard library. Without the “using namespace std;” line this would have been called as std::cout. It is defined in the iostream header file. << is the C++ insertion operator. It is used to pass characters from the right to the object on the left. endl is the C++ newline character. Slight change  Let’s put the message into some variables of type string and print some numbers.  Things to note:  Strings can be concatenated with a + operator.  No messing with null terminators as in C  Some string notes:  Access a string character by brackets or function:  msg[0]  “H” or msg.at(0)  “H”  C++ strings are mutable – they can be changed in place.  Press F9 to recompile & run. #include using namespace std; int main() { string hello = "Hello"; string world = "world!"; string msg = hello + " " + world ; cout << msg << endl; msg[0] = 'h'; cout << msg << endl; return 0; } Basic Syntax  C++ syntax is very similar to C, Java, or C#. Here’s a few things up front and we’ll cover more as we go along.  Curly braces are used to denote a code block: { … some code … }  Statements end with a semicolon: int a ; a = 1 + 3 ;  Comments are marked for a single line with a // or for multilines with a pair of /* and */ : // this is a comment. /* everything in here is a comment */  Variables can be declared at any time in a code block. void my_function() { int a ; a=1 ; int b; }  Functions are sections of code that are called from other code. Functions always have a return argument type, a function name, and then a list of arguments: int my_function(int x) { return x ; } // No arguments? Still need () void my_function() { /* do something... but a void value means the return statement can be skipped.*/ }  Variables are declared with a type and a name:  A sampling of Operators: + - * / % ++ && (AND) ||(OR) !(NOT)  Arithmetic:  Logical:  Comparison: == > < >= <= != -- // Usually enter the type int x = 100; float y; vector vec ; // Sometimes it can be inferred auto z = x; Built-in (aka primitive or intrinsic) Types  “primitive” or “intrinsic” means these types are not objects  Here are the most commonly used types.  Note: The exact bit ranges here are platform and compiler dependent!  Typical usage with PCs, Macs, Linux, etc. use these values  Variations from this table are found in specialized applications like embedded system processors. Name Name Value Name Value char unsigned char 8-bit integer float 32-bit floating point short unsigned short 16-bit integer double 64-bit floating point int unsigned int 32-bit integer long long 128-bit integer long unsigned long 64-bit integer long double 128-bit floating point bool true or false Need to be sure of integer sizes?    In the same spirit as using integer(kind=8) type notation in Fortran, there are type definitions that exactly specify exactly the bits used. These were added in C++11. These can be useful if you are planning to port code across CPU architectures (ex. Intel 64-bit CPUs to a 32-bit ARM on an embedded board) or when doing particular types of integer math. For a full list and description see: http://www.cplusplus.com/reference/cstdint/ #include Name Name Value int8_t uint8_t 8-bit integer int16_t uint16_t 16-bit integer int32_t uint32_t 32-bit integer int64_t uint64_t 64-bit integer Type Casting  C++ is strongly typed. It will auto-convert a variable of one type to another in a limited fashion: if it will not change the value. short x = 1 ; int y = x ; // OK short z = y ; // NO!   Conversions that don’t change value: increasing precision (float  double) or integer  floating point of at least the same precision. C++ allows for C-style type casting with the syntax: (new type) expression double x = 1.0 ; int y = (int) x ; float z = (float) (x / y) ;  In addition to this C++ offers 4 different variations in a C++ style. Type Casting  static_cast( expression )  This is exactly equivalent to the C style cast.  This identifies a cast at compile time and the compiler inserts the CPU type conversion instructions for primitive types.  Can do casting that reduces precision (ex. double  float)  dynamic_cast( expression)  Special version where type casting is performed at runtime, only works on reference or pointer type variables.  const_cast( expression )  Variables labeled as const can’t have their value changed.  const_cast lets the programmer remove or add const to reference or pointer type variables.  reinterpret_cast( expression )  Takes the bits in the expression and re-uses them unconverted as a new type. Also only works on reference or pointer type variables. “unsafe”: the compiler will not protect you here. Functions  Open the project “FunctionExample” in C::B files        The values of L and W are sent to the function, multiplied, and the product is returned. RectangleArea2 uses const arguments  The function arguments L and W are sent as type float. float RectangleArea1(float L, float W) { return L*W ; } Compile and run it! Open main.cpp 4 function calls are listed. The 1st and 2nd functions are identical in their behavior.  The return type is float. The compiler will not let you modify their values in the function. Try it! Uncomment the line and see what happens when you recompile. 3rd 4th The and versions pass the arguments by reference with an added & Product is computed float RectangleArea2(const float L, const float W) { // L=2.0 ; return L*W ; } float RectangleArea3(const float& L, const float& W) { return L*W ; } void RectangleArea4(const float& L, const float& W, float& area) { area= L*W ; } Using the C::B Debugger   To show how this works we will use the C::B interactive debugger to step through the program line-by-line to follow the function calls. Make sure you are running in Debug mode. This turns off compiler optimizations and has the compiler include information in the compiled code for effective debugging. Add a Breakpoint  Breakpoints tell the debugger to halt at a particular line so that the state of the program can be inspected.  In main.cpp, double click to the left of the lines in the functions to set a pair of breakpoints. A red dot will appear.  Click the red arrow to start the code in the debugger.  The debugger will pause in the first function at the breakpoint.   Click the Debug menu, go to Debugging Windows, and choose Call Stack. Drag it to the right, then go back and choose Watches. Drag it to the right. Do the same for the Breakpoints option. Your screen will look something like this now… Controls (hover mouse over for help): Watches shows the variables in use and their values Call Stack shows the functions being called, newest on top. Place the cursor in the function, click to run to the cursor Run the next line Step into a function call Step out of a function to the calling function. Breakpoints lists the breakpoints you’ve created. Step by CPU instruction. Less useful, generally.