Summary of what we learned yesterday Basics of C++ Format of a program Syntax of literals, keywords, symbols, variables Simple data types and arithmetic operations Assignment operator Today we will look at: Standard input (cin) and output (cout) More data types More complex arithmetic operations More on assignment operator

Announcements HW1 will be assigned this week at SUCourse Due October 7 Wednesday at 17:00 For homework assignments and submissions, we are using SUCourse Homework will be explained in recitations Moreover, there will be important explanations about the homework submission procedure in recitations Submission is a tricky process, please do attend the recitations in order not to make a mistake No late homework without penalty One late day is allowed at cost of 10% of full grade Plagiarism is not tolerated Homeworks are to be done personally we use software tools to detect plagiarized homework first case –100 (minus hundred), second fails the course! detailed policy is on the web site of the course Two Midterm Exams + Final Exam Midterm 1: November 7 th Saturday 14:00 – 16:00 Midterm 2: December 5 th Saturday 10:00 – 12:00

Data Types string used it in previous lectures more technically, string is a class char for single character digits, letters, symbols uses up one byte range why? one byte (8 bits) can store 2 8 = 256 different values. stores the code of the character e.g. 65 for ‘A’ character arithmetic is possible (will see later) char literals are in single quotes (strings are in double quotes ") 'z' 'T' '4' '&' bool boolean (will see later)

Numeric Types to represent integer and real numbers int integer numbers no infinity in computers  limited range 2 or 4 bytes (16 or 32 bits) depending on the computer and compiler you use in our case: 4 bytes (32 bits) integer range: – 32, ,767 for 16-bit computers why? –2,147,483, ,147,483,647 for 32-bit computers why?

Numeric Types (cont’d) short int (or just short ) always 16-bit integer long int (or just long ) always 32-bit integer signed versus unsigned integers you can put signed or unsigned keywords before the type we discussed signed integers signed is default unsigned integers use the same amount of bits but ranges are different 16-bit: ,535 (2 16 –1) 32-bit: ,294,967,295 (2 32 –1)

Numeric Types (cont’d) Real numbers in C++ Real literals e21 Real data types (their difference is in precision) float consumes 4 bytes Range: 0 U [ e– e+38] U [ e– e+38] Tapestry does like float double consumes 8 bytes Range: 0 U [ e– e+308] U [ e– e+308] Standard but a bit complex representation see “floating point representation” item in MSDN Library index:

More on C++ types Check out these items in MSDN Library Index Fundamental types more on C++ types LIMITS.H header file (Microsoft Visual Studio\VC98\Include) limits of integer and char types MSDN help on Integer Limits floating limits (FLOAT.H) limits for the floating points numbers (float, double) MSDN help on Floating Limits floating point representation if you are interested in to learn how the real numbers are represented in computers MSDN help

Arithmetic Operations Operators: + - * / % Operands: values that operator combines variables or literals Combination of operators and operands is called expression Syntax and semantics for arithmetic operations: Addition Subtraction MultiplicationDivisionModulus * 421 / 4 is 5 x + yx * / 4.0 is % 2 is 0 d – d * 23.1 * 4x / 4x % – 3 * 2x / yx % y

Arithmetic Operations (cont’d) Mixed type expressions what if one operator is int other is double? integer is converted into double before operation 5.0 * 8 is / 10 is 0 (integer division) 5.0 / 10 is 0.5 (real division) 10 – 8is 2 (integer) 10 – 8.0 is 2.0 (double)

Expressions with several operators You can use parentheses in expressions to group them Open ( and close ) parentheses should match Rule 1: Parenthesized sub-expressions are evaluated first inside to out Rule 2: Within an expression/subexpression if there are several operators, use operator precedence, evaluate * / % before + - Rule 3: If the operators are in the same expression/subexpression and at the same precedence level, then associativity rule applies evaluate operators from left-to-right Examples (5 - 3 * (7 - 3)) * 8 is / 2 * 6 / 2 + (5 - 3 * (2 - 1)) is 17

Expressions with several operators Are the following expressions equivalent? (40 – 32) * 5 / 9 (40 – 32) * (5 / 9) NO, first one is 4, second one is 0 What about this? (40 – 32.0) * 5 / 9 Operations are double operations. Result is Are these operators sufficient? how to calculate square root? Later we’ll study functions like sqrt, cos, sin, pow, … For complicated mathematical operations that you cannot easily do using basic operators Accessible using #include (or )

Integer vs. Real Real values can be assigned to Integer variables, but this is not recommended since we loose precision int a; double r; r = ; a = r; What is the value of a?  125 Real value is truncated before storing in an integer variable Avoid doing this VS 2010 Compiler warns you but does not give error Be careful when passing arguments to parameters as well passing an integer argument to a double parameter causes the same precision problem

Integer vs. Real (More on Precision) What is the difference between red and blue parts in the following program (fahrcels.cpp)? red: integer arithmetic (low precision) blue: real arithmetic (high precision) int main() { int ifahr; double dfahr; cout << "enter a Fahrenheit temperature "; cin >> ifahr; cout << ifahr << “ F = “ << (ifahr - 32) * 5/9 << " Celsius" << endl; cout << "enter another temperature "; cin >> dfahr; cout << dfahr << “ F = “ << (dfahr - 32) * 5/9 << " Celsius" << endl; return 0; } See Figure 3.4 in the textbook.

Overflow See daysecs.cpp Overflow occurs when the result of an integer expression is outside the limits Run the program with 365 days result: seconds  correct result and output days result: seconds  correct result and output days result: seconds  incorrect result and output due to overflow days result: seconds  incorrect result and output due to overflow

More on Assignment operator (4.1 & 4.3.4) Assignment operator is = to store values in variables variable = expression; first the right hand side expression is evaluated using the current values then the evaluated expression is stored in variable Types should be compatible, otherwise a syntax error may occur (e.g. string variable, integer expression), or precision is lost (e.g. integer variable, real expression) Example: what is the value of a after the assignment? int a, b; b = 25; a = 8; a = b – 3 * a + 2; Answer: 3 A rule: Right hand side expression is evaluated before the assignment operator is executed. If you use the left hand side variable in the right hand side expression as well, then the current value is used in the expression. See Program 4.1 in textbook.

More on Assignment operator (4.1 & 4.3.4) Assigning single expression to several variables variable 1 = variable 2 = variable 3 =... variable n = expression; all variables are assigned the same value of expression example: int x, y, z; x = y = z = 5; x, y and z contain 5 Arithmetic assignment operators += -= *= /= %= Combines arithmetic operation and assignment in one operator variable += expression is the same as variable = variable + expression Example: x += 1 is the same as x = x + 1 Same for -= *= /= and %= x -= 1 x *= 3 x /= 2 and x %= 2