Understanding Arithmetic Operations and Variable Declaration in C++

1. Chapter 3 Arithmetic Operations

2. Review • function • statement • input/output • comment • #include • data type • variable • identifier • constant • declaration

3. Declaration Statements • Variable: a memory location to store data • Variable value: the content in the location • Identifier: the symbolic name of a variable • Data Type: the type of data the variable is for • A declaration tells the compiler to allocate enough memory to hold a value of this data type and to associate the identifier with this location string name; DataType Identifier , Identifier, … ; string firstName, lastName; int num = 10;

4. Arithmetic Operations

5. Add Two Numbers In Math S = x + y Or x + y = S How to add two numbers in C++?

6. Assignment Operator: = num1 + num2 = sum; // Valid in C++? // No • Assignment statement MUST be from right to left sum = num1 + num2; // Correct! // Not “equal” • Assignment statement: variable = expression;

7. Are the two statements the same? Sum = Num1 + Num2; Sum = num1 + num2; // NO! // C++ is case sensitive!

8. Arithmetic Operators • Addition: + • to compute Sum • Subtraction: - • to compute Difference • Multiplication: * • to compute Product • Division: / • to compute Quotient • Modulus: % • to compute the remainder from integer division You MUST use operators to compute in C++!

9. Arithmetic Operators • What is ** in C++? result = x ** y; // Not good! • What is ^ in C++? result = x ^ y; // Not good! S = x ( y + z); //Is it good in C++? //Missing operator! S = x * ( y + z); // Good!

10. Unary Operator • Unary operator: operator that has only one operand validCount++; // validCount = validCount + 1; totalCount --; // totalCount = totalCount - 1; • Binary operator: operator that has two operands num1 + num2

11. Semantics, Syntax, and Style total = total + 2; • Semantics Increase total by 2 Assignment (right to left) Not equal • Syntax Statement terminator Case sensitive • Style one space before and after any operator meaningful name

12. Precedence Rules • From high to low: • ( ) • *, /, % • +, -

13. Examples x = 8 - 4 * 2; // result: x = (8 - 4) * 2; // result: y = 8 / 4 * 2; // result: y = 8 / (4 * 2); // result:

14. More Examples z = 8 / 4 ^ 2; // No! z = 8 / 4 ** 4; // No! z = 8 / 4 * 4 // Result: ? X = 5(3 – 7); //Result: ? z = 5 / (2 * 5); // Result: 0.5 or 0?

15. Integer Division vs. Float Division In Math 5 is almost always the same as 5.0 In C++ 5 is almost never the same as 5.0 Why? Store value in computer as bits, bytes. 5 is stored as an integer 5.0 is stored as a float number

16. Integer Division We can only get integers! 7 / 5 Quotient: 1 Remainder: 2 5 / 7 Quotient: 0 Remainder: 5

17. Float Division We get float result! 7.0 / 5.0 Quotient: 1.4 7 / 5.0 (Same) 7.0 / 5 (Same) 5.0 / 7 Quotient: 0.714285… As long as there is a float number in the expression, the result is a float number.

18. The Cast Functions int num1, num2; float quotient; cin >> num1 >> num2; quotient = num1 / num2; // what’s the value of quotient? // How to get float quotient? quotient = float(num1) / num2; // Use cast function float(variable) quotient = float(num1 / num2); // Integer division or float division? // Integer division!

19. Quotient (Division) Operator: / Result 1 0 2 0 14 0 Expression 7 / 5 5 / 7 14 / 5 5 / 14 143 / 10 10 / 143

20. Remainder (Modular) Operator: % Result 2 5 4 5 3 10 Expression 7 % 5 5 % 7 14 % 5 5 % 14 143 % 10 10 % 143

21. Exercises Expression Result 12 % 20 * 3 (12 % 20) * 3 12 * 3 20 % 12 * 3 12 / 20 * 3 20 / 12 * 3 20 / 12 % 3 20 % 12 % 3

22. Why Integer Division? after class exercise: write this solution into a C++ program Get $143 from ATM 143 / 50 Number of $50 bills: 2 143 % 50 Amount left after $50 bills: 43 43 / 10 Number of $10 bills: 4 43 % 10 Amount left after $10 bills: 3 Number of $1 bills: 3

23. Summary • Assignment Operator total = total + num1; // from right to left • Arithmetic Operators and Precedence Rules () /, %, * -, + • Semantics, Syntax, and Style