1. CS 6301 Lecture 2: First Program1

2. CS 630 2 Topics of this lecture Introduce first program  Explore inputs and outputs of a program Arithmetic using C++ Introduce the conditional statement

3. CS 630 3 General Notes About C++ and This Book Book geared toward novice programmers  Stress programming clarity  C and C++ are portable languages Portability  C and C++ programs can run on many different computers Compatibility  Many features of current versions of C++ not compatible with older implementations

4. CS 630 4 Introduction to C++ Programming C++ language  Facilitates structured and disciplined approach to computer program design Following several examples  Illustrate many important features of C++  Each analyzed one statement at a time Structured programming Object-oriented programming

5. CS 630 5 A Simple Program: Printing a Line of Text Comments  Document programs  Improve program readability  Ignored by compiler  Single-line comment Begin with // Preprocessor directives  Processed by preprocessor before compiling  Begin with #

6. CS 630 6 Basics of a Typical C++ Environment Input/output  cin Standard input stream Normally keyboard  cout Standard output stream Normally computer screen  cerr Standard error stream Display error messages

7. CS 630 7 fig01_02.cpp (1 of 1) fig01_02.cpp output (1 of 1) 1 // Fig. 1.2: fig01_02.cpp 2 // A first program in C++. 3 #include 4 5 // function main begins program execution 6 int main() 7 { 8 std::cout << "Welcome to C++!\n"; 9 10 return 0; // indicate that program ended successfully 11 12 } // end function main Welcome to C++! Single-line comments.Preprocessor directive to include input/output stream header file. Function main appears exactly once in every C++ program. Function main returns an integer value. Left brace { begins function body. Corresponding right brace } ends function body. Statements end with a semicolon ;. Name cout belongs to namespace std. Stream insertion operator. Keyword return is one of several means to exit function; value 0 indicates program terminated successfully.

8. CS 630 8 A Simple Program: Printing a Line of Text Standard output stream object  std::cout  “Connected” to screen  << Stream insertion operator Value to right (right operand) inserted into output stream Namespace  std:: specifies using name that belongs to “namespace” std  std:: removed through use of using statements Escape characters  \  Indicates “special” character output

9. CS 630 9 A Simple Program: Printing a Line of Text Make some modifications to First Program

10. CS 630 10 Another Simple Program: Adding Two Integers Variables  Location in memory where value can be stored  Common data types int - integer numbers char - characters double - floating point numbers  Declare variables with name and data type before use int integer1; int integer2; int sum;  Can declare several variables of same type in one declaration Comma-separated list int integer1, integer2, sum;

11. CS 630 11 Another Simple Program: Adding Two Integers Variables  Variable names Valid identifier  Series of characters (letters, digits, underscores)  Cannot begin with digit  Case sensitive Naming Conventions  start with a lower case letter  mix of lower and uppercase letters and numbers  short but meaningful  generally avoid single letter variables

12. CS 630 12 Another Simple Program: Adding Two Integers Input stream object  >> (stream extraction operator) Used with std::cin Waits for user to input value, then press Enter (Return) key Stores value in variable to right of operator  Converts value to variable data type = (assignment operator)  Assigns value to variable  Binary operator (two operands)  Example: sum = variable1 + variable2;

13. CS 630 13 1 // Fig. 1.6: fig01_06.cpp 2 // Addition program. 3 #include 4 // function main begins program execution 5 int main() { 6 int integer1; // first number to be input by user 7 int integer2; // second number to be input by user 8 int sum; // variable in which sum will be stored 9 10 std::cout << "Enter first integer\n"; // prompt 11 std::cin >> integer1; // read an integer 12 13 std::cout << "Enter second integer\n"; // prompt 14 std::cin >> integer2; // read an integer 15 16 sum = integer1 + integer2; // assign result to sum 17 std::cout << "Sum is " << sum << std::endl; // print sum 18 19 return 0; // indicate that program ended successfully 20 } // end function main Declare integer variables.Use stream extraction operator with standard input stream to obtain user input. Stream manipulator std::endl outputs a newline, then “flushes output buffer.” Concatenating, chaining or cascading stream insertion operations. Calculations can be performed in output statements: alternative for lines 16 and 17: std::cout << "Sum is " << integer1 + integer2 << std::endl; fig01_06.cpp (1 of 1)

14. CS 630 14 Microsoft Visual C++ numeric data types Type NameBytesOther NamesRange of Values int*signed, signed intSystem dependent unsigned int*unsignedSystem dependent __int81char, signed char–128 to 127 __int162short, short int, signed short int –32,768 to 32,767 __int324signed, signed int–2,147,483,648 to 2,147,483,647 __int648none–9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 char1signed char–128 to 127 unsigned char1none0 to 255

15. CS 630 15 Type Name BytesOther NamesRange of Values short2short int, signed short int–32,768 to 32,767 unsigned short2unsigned short int0 to 65,535 long4long int, signed long int–2,147,483,648 to 2,147,483,647 unsigned long4unsigned long int0 to 4,294,967,295 enum*noneSame as int float4none3.4E +/- 38 (7 digits) double8none1.7E +/- 308 (15 digits) long double10none1.2E +/- 4932 (19 digits) Microsoft Visual C++ numeric data types

16. CS 630 16 Memory Concepts Variable names  Correspond to actual locations in computer's memory  Every variable has name, type, size and value  When new value placed into variable, overwrites previous value  Reading variables from memory nondestructive

17. CS 630 17 Memory Concepts std::cin >> integer1;  Assume user entered 45 std::cin >> integer2;  Assume user entered 72 sum = integer1 + integer2; integer1 45 integer1 45 integer2 72 integer1 45 integer2 72 sum 117

18. CS 630 18 Effect of Several Assignments What are the values of a and b after all statements are executed? int a = 1; int b; b = a; a = 2; a = 2, b = 1

19. CS 630 19 Arithmetic Arithmetic calculations  * Multiplication  / Division Integer division truncates remainder  7 / 5 evaluates to 1  % Modulus operator returns remainder  7 % 5 evaluates to 2

20. CS 630 20 Arithmetic Rules of operator precedence  Operators in parentheses evaluated first Nested/embedded parentheses  Operators in innermost pair first  Multiplication, division, modulus applied next Operators applied from left to right  Addition, subtraction applied last Operators applied from left to right X = 7 + 4 / 2 * (3 * ( 4 – 3) + 5) % 2 + 3

21. CS 630 21 Decision Making: Equality and Relational Operators if structure  Make decision based on truth or falsity of condition If condition met, body executed Else, body not executed Equality and relational operators  Lower precedence than arithmetic operators  Equality operators Same level of precedence  Relational operators Same level of precedence  Associate left to right

22. CS 630 22 Decision Making: Equality and Relational Operators Notice: “==“ (not “=“)

23. CS 630 23 using statements Eliminate the need to use the std:: prefix Allow us to write cout instead of std::cout To use the following functions without the std:: prefix, write the following at the top of the program  using std::cout;  using std::cin;  using std::endl; Look at example program