1 More C++ Basics Chapter 3 Lecture CSIS 10A

2 Agenda Review  C++ Standard Numeric Types Arithmetic–way more than you want! Character (char) data type For Loop Syntax, Run-time and Logical Errors

3 Review: Standard Program Structure To solve most problems, your main() program will generally look like this (conceptually) 1.Declare variables for input, result and intermediate data 2.Ask for data (cout) 3.Input data (cin) 4.Calculate result 5.Output result (cout)

4 An interactive C++ program: //circle.cpp Calculate area of a circle // given a radius value #include using namespace std; int main() {int area, radius; cout << "enter a radius: "; cin >> radius; area = radius * radius * 3.14; cout << "the area is " << area << endl; return 0; }

5 A small problem… Run circle.cpp: But according to our code, it should be 3.14 What happened? enter a radius: 1 the area is 3 Press any key to continue...

6 We used the wrong data type! Go back, change: int area, radius; To: float area, radius; Now it works…the lesson? 1) Data types are important! 2) Testing is important!

7 Agenda Review C++ Standard Numeric Types  Arithmetic–way more than you want! Character (char) data type For Loop Syntax, Run-time and Logical Errors

8 Basic C++ Data Types int – Represents integers float – Represents real (floating point) numbers char – Represents characters (single letters)

9 Integers only store whole numbers int a=4; // puts 4 in a int a= ; // puts 4 in a INTS are great for loop counters, representing inventory, numbers of “things”

10 Trivia—other integer types uses range of values short (2 bytes)….-32,767 to long …….….(4 bytes)…-2 bill to +2 billion int ………….(depends)…long (sometimes short) unsigned short (2 bytes)…0 to unsigned long...(4 bytes) …0 to 4 billion

11 Beware Integer wraparound // wrap.cpp int a, b, c; a = ; b = 2 * a; c = 3 * a; cout << "b is " << b << endl; cout << "c is " << c << endl; b is c is

12 FLOATING-POINT Types float is used to represent numbers with a fractional part such as or 6.45 etc… or really big numbers that won’t fit inside ints uses range precision float (4 bytes)…… to ……..6 digits double…...(8 bytes)…… to …...15 digits long double (10 bytes) to …19 digits

13 What does floating point mean? Consider a number like “Float” the point so that all the digits are on its right (here the point is shifted 3 digits to the left) = x 10 3 E-notation: the letter ‘e’= “x10 to the power of” You can actually enter or display data using ‘e’: same as e3 same as e2

14 Fine…. How is this stored in a float variable ?? The mantissa and the exponent 3 are stored separately (in a variable) For a 32 bit float type : 23 bit mantissa + 8 bit exponent + 1 sign bit For a 64 bit double type : 52 bit mantissa + 11 bit exponent + 1 sign bit

15 Implications for Accuracy (round-off error) A float only stores about 6 digits of mantissa float PI= ; PI really contains float x= , y= ; x=x+y; DOES NOT CHANGE X!!! (no room) Use a double if you need more precision double PI= ; About 16 digits of mantissa double x= , y= ; x=x+y; DOES CHANGE X!!! (now there’s room)

16 Q1) Practice your Scientific Notation (answers at end of slides) = ____________ x 10 ____.03413= ____________ e ____ 6.78 x 10 7 = ____________ 5.32e-5 = ____________

17 Displaying Floating Point data cout << 4.5 << endl; cout << << endl; cout << << endl; cout << << endl; cout << << endl; cout << << endl; cout << << endl; Output e e e-05 This is an integer, no ‘.’

18 Formating Floating Point Output cout<<fixed<<showpoint<<setprecision(2); cout << 4.5 << endl; cout << << endl; cout << << endl; cout << << endl; cout << << endl; cout << << endl; cout << << endl; You can use this on problem 8 Output For this to work, #include

19 Constants are “variables” -- that never change Use the keyword “const” in front of declaration You MUST provide initial value at declaration const double PI= ; const double METERS_PER_YARD = ; const int MAX=1000; Now you can say: area = PI * radius * radius; Don’t over do it: const int SECONDS_PER_MINUTE = 60; You can use a constant for problem 7

20 Agenda Review C++ Standard Numeric Types Arithmetic–way more than you want!  Character (char) data type For Loop Syntax, Run-time and Logical Errors

21 Arithmetic in C++ Basic operations + - * / Math formulas need to be converted into C++ syntax: FORMULA Equivalent C++ A =  r 2 area=3.14*radius*radius; F = (v -a) force=(v-a)/(v+a); (v+a)

22 More C++ Math Formulas

23 Arithmetic -- Order of Precedence * and / are done first, then + and – Equal levels are done left to right Example: 3 * = * 4 = / = = = 11 Parentheses have highest precedence (use if you want different order) (6 + 4) / (2 + 3) = 2

24 Q2) Practice Arithmetic Precedence Evaluate the following 1+2 * = _______ / 2 * 3 = _______ * (3 + 4) = _______ (7 + 5) / (2 * 3)= _______

25 Mixed-type Expressions Expressions involving int and float will give a result of type float (the most inclusive type) Suppose you have int n; float x; Then n + x  results in float n * 4  results in int n  results in double (4.0 is double) (default for floating pt literals)

26 Mixed-type Assignments Assigning int to float is perfectly safe Assigning float to int may lose fractional part Suppose you have int n; float x; Then 1.x = 15;  stores 15 in x 2.n = 4.5;  stores 4 in n -- Compiler Warning! To satisfy the compiler for (2.) simply explain your intentions: n = int(4.5);

27 Q3) Can you guess what is stored in these variables? int m, n; double x,y; m = 3.0; n = 12.7; x = m; x = x m = m + 1; y = x + 1; mnxy ????

28 Integer Division CAUTION—this is a common C++ error When both sides are int, the result MUST be int 9 / 2 = 4 9 / 10 = 0 Sometimes this is what we want (convert inches to inches and feet) Usually causes programming errors When one side is float, the answer is float 9 / 2.0 = / 10 = 0.9

29 Q4) Can you guess what is stored in these variables? int m, n; double x,y; m = 10 / 3; n = 30 / 7; x = n * m; y = 3 / 4 * x; y = x * 3 / 4; y = (x + 3) / 4; mnxy ????

30 One more thing…type-casting If you want to perform floating point division on a pair of integer variables, you can…but you have to temporarily convert one of them to float first: int m=3, n=4; float y; y = float(m) / n; ( y = 0.75) WRONG y = float(m/n); ( y = 0)

31 Break Time! Download Lab2MoreBasics.cpp Work on problems 1-4, 7,8 Call me over if you have questions

32 Remainder % operator The expression 10 / 3 gives the quotient, 3 We use 10 % 3 to get the remainder, 1 4 / 3 = 112 % 6 = 0 4 % 3 = 1 13 % 6 = ____ 2 / 3 = 014 % 6 = ____ 2 % 3 = 223 % 7 = _____ Only use % on integers

33 What good is % operator? You can use it to subdivide something into hierarchical units: int feet, inches; cout << "Enter inches: "; cin >> inches; feet = inches / 12; inches = inches % 12; cout << feet << " ft. " << inches << " in."; This is used in things like time, weight, length, change, etc. Use this slide on Problem 9 Enter inches: 75 6 ft. 3 in.

34 Arithmetic Assignment Operators Numeric operators +, -, *, /, % can be combined with the assignment operator = Saves time and typing Only when you want to store result in one of operands a += b  a = a + b a -= b  a = a - b a *= b  a = a * b a /= b  a = a / b a %= b  a = a % b

35 Q5) Arithmetic Assign Operator Table START: int x=0; ShorthandSame asResult x+=5; x*=2; x/=5; x-=2; x+=10; x*=3; x%=8 x/=5; x=x+5; x=x*2; x=x/5; x=x-2;

36 Agenda Review C++ Standard Numeric Types Arithmetic–way more than you want! Character (char) data type  For Loop Syntax, Run-time and Logical Errors

37 CHARACTER types (see Lab3-1) char……………... (1 byte) unsigned char…….(1 byte) A char stores a single letter What is actually stored is the binary sequence corresponding to a letter’s ASCII code You can either store a letter, or the numeric code for the letter in a char

38 Check this out…. #include void main() {both a and c contain 65 or ‘A’ char a = 65, c = 'A'; cout << “ c = “ << c << endl; cout << “ a = “ << a << endl; } Output….. c = A a = A (in other words, ‘A’ is same as 65)

39 Decimal ASCII Table

40 Character Input Read 2 chars char grade1, grade2; cin>>grade1>>grade2; cout<<“Grade 1 is ”<<grade1<<endl; cout<<“Grade 2 is ”<<grade2<<endl; NOTE white space ignored: type AB, A B, A (enter) B  same result Another interesting topic, character escape and control sequences, p 53/54

41 Agenda Review C++ Standard Numeric Types Arithmetic–way more than you want! Character (char) data type For Loop  Syntax, Run-time and Logical Errors

42 Bored with single execution programs? Add a for loop to repeat your code several times: for (int k=1; k<=final_value; k=k+1) { statements to repeat }

43 Example Looped code Add a for loop to repeat your code several times: int main() { for (int k=1; k<=3; k=k+1) { cout<<“Testing”<<k<<endl; } Testing 1 Testing 2 Testing 3 Or k++ for short

44 Example Application (for challenge) Calculate pay for 3 employees: int hrs; double rate; for (int emp=1; emp<=3; emp++) { cout<<“Enter hours & rate: ”; cin>> hrs>> rate; cout<<“Pay = $”<< hrs * rate <<endl; } See p57 to let user determine the number of iterations

45 Agenda Review C++ Standard Numeric Types Arithmetic–way more than you want! Character (char) data type For Loop Syntax, Run-time and Logical Errors 

46 Types of Errors Syntax: an error in your C++ language/grammar (covered last week) confuses compiler (The dog his paw) forgetting a ; misspelling a variable name datha=3.14; Runtime: when you do something illegal during program execution temp=0.0; rate=1.0/temp; // dividing a number by zero –crash! Logical (or Semantic): When you say something illogical A paw ate his dog. ( Good grammar, illogical meaning) avg = b + c / 2;

47 Tracking them down Syntax— double click on error message, it takes you to line of code Look at or above that line for possible errors Runtime & Logical You detect them by checking output against test plan Pinpoint them by displaying variables during intermediate steps (cout) OR Use debugger to step through program, put watch on variables

48 LIST OF KEYWORDS….. asm auto bool break case catch char class const const_cast continue default delete do double dynamic_ cast else enum explicit export extern false float for friend goto if inline int long mutable namespace new operator private protected public register reinterpret _cast return short signed sizeof static static_cast struct switch template this throw true try typedef typeid typename union unsigned using virtual void volatile wchar_t while

49 That’s a wrap ! What we learned today: Data Types Rules of Arithmetic For loops How to debug your program

50 A1) Answers to Scientific Notation = x = e x 10 7 = e-5 =

51 A2) Arithmetic Precedence Evaluate the following 1+2 * = / 2 * 3 = * (3 + 4) = 15 (7 + 5) / (2 * 3)= 2

52 A3) Answer: int m, n; double x,y; m = 3.0; n = 12.7; x = m; x = x m = m + 1; y = x + 1; mnxy ????

53 A4) Integer Division int m, n; double x,y; m = 10 / 3; n = 30 / 7; x = n * m; y = 3 / 4 * x; y = x * 3 / 4; y = (x + 3) / 4; mnxy ????

54 A5) Arithmetic Assign Operator Table START: int x=0; ShorthandSame asResult x+=5; x*=2; x/=5; x-=2; x+=10; x*=3; x%=8 x/=5; x=x+5; x=x*2; x=x/5; x=x-2; x=x+10; x=x*3; x=x%8; x=x/5;