ECE 1305 Introduction to Engineering and Computer Programming

1. ECE 1305Introduction to Engineering and Computer Programming Section 05Variables, Data Types and Operators

2. Variables • Variables must be named with a valid identifier. • Must start with a letter or an underscore • Must contain only letters, digits, or the underscore. • C++ is case sensitive • myvariable and Myvariable are two different identifiers.

3. Identifiers • It is common C++ practice to: • name functions with all lowercase letters interest() • name variables with initial lowercase letters the uppercase letters to separate words variableInterestRate; • name constants with all uppercase INTEREST_RATE;

4. Variable Declarations • All variables must be explicitly declared. • This forces the programmer to design the program before coding. • A variable declaration has the form Type_Name Variable_Name; • Examples int numberOfBeans double weightOfBeans

5. Variable Declarations • Variable declarations do two things: • Name the variable • Instructs the compiler to set aside memory space for the variable • Different variable types have different memory requirements. • Operators may perform differently depending on the data type.

6. Data Types • All numbers are not created equal. Different types of numbers have different memory requirements. • Functions and operators act on specific types of numbers and return results of a specific number type. • Only numbers in a certain range can be represented in a computer. A calculation may result in an overflow error.

7. short 15 bits ( – 32,767 ... 32,767 ) Sign (1 bit) unsigned short 16 bits ( 0 ... 65,535 ) 31 bits int ( – 2,147,483,647 ... 2,147,483,647 ) Sign (1 bit) 32 bits unsigned long ( 0 ... 4,294,967,295 ) Integer Types

8. Floating Point Representation • An non-integer number may be approximated by the form mantissa 2 exponent • For example 0.11001001  2 00000101 which equals 0.78515625  2 5 = 25.125 in Decimal • All floating point numbers stored in a computer memory are only approximations.

9. float (Single Precision) 8 bits 23 bits exponent fraction Sign (1 bit) (  10 –37 ... 10 38 with 7 significant digits of accuracy ) Sign (1 bit) 11 bits 20 bits double (Double Precision) exponent fraction 32 bits fraction (  10 –307 ... 10 308 with 15 significant digits of accuracy ) Floating Point Types

10. The Assignment Operator • The assignment operator assigns a value to a variable. • The expression on the right-hand side of the equal sign is evaluated. The resulting value is assigned to the memory location identified on the left-hand side of the equal sign.

11. The Assignment Operator • Example: double temperature; temperature = 98.6; double distance, rate, time; rate = 100.0; time = 3.2; distance = rate * time;

12. The Assignment Operator • The assignment operator is not the same as the mathematical equality sign. int n; n = n + 1; • new_value = old_value + increment

13. Uninitialized Variables • When a variable is declared it is not assigned a value. The programmer cannot assume it starts with a value of zero! • The memory location may hold garbage. • Variables may be assigned a value when they are declared. int numberOfBeans = 6237; double weightOfBeans = 25.87;

14. Basic Mathematical Operators * multiplication / division % remainder (modulo division) + addition - subtraction = assignment

15. Arithmetic Operator Precedence • Mathematical Operations are performed with the following precedence. Parentheses used to group expressions (...) Unary + , Unary – Multiplication * , Division / , Modulo Division % Binary + , Binary – Assignment = • Binary Operators of equal precedence are evaluated from left – to – right.

16. Priority of Operators double answer = 4.8 / -2.0 + (8.5 – 12.0 * 0.5) * 10.0; 4.8 / -2.0 + (8.5 – 12.0 * 0.5) * 10.0 4.8 / -2.0 + (8.5 – 12.0 * 0.5) * 10.0 4.8 / -2.0 + (8.5 – 6.0) * 10.0 4.8 / -2.0 + 2.5 * 10 4.8 / -2.0 + 2.5 * 10 -2.4 + 25 Results in the variableanswer assigned the value 22.6

17. Combined Operators • C++ allows the assignment operator to be combined with other mathematical operators.

19. Integer Division int a = 38; int b = 7; int z = 38/7; Results in the variable z assigned the value 5 int a = 38; int b = 7; int z = 38%7; Results in the variable z assigned the value 3

20. Automatic Conversion of Data Types int k = 5, m = 4, n; double x = 1.5, y = 2.1, z; z = k + x; k is promoted to a double and added to x z is assigned the value 6.5 n = k + x; k is promoted to a double and added to x n is assigned the value 6, the assignment operator converts the number to int and the fraction is lost

21. Automatic Conversion of Data Types int k = 5, m = 4, n; double x = 1.5, y = 2.1, z; z = m * y; m is promoted to a double and multiplied with y The variable z is assigned the value 8.4 n = x * y; The variable n assigned the value 3 The assignment operator converts the number to int and the fraction is lost.

22. Explicit Conversion of Data Types int k = 5, m = 4, n; double z; z = k / m; The variable z assigned the value 1.0

23. Data Type Conversion • An expression my be converted from one data type to another. int k = 5, m = 4, n; double z; z = double(k) / double(m); k and m are converted to double before the division. The variable z is assigned the value 1.25

24. Rounding Numbers cout << int(15.6) << endl; 15 cout << int(15.6 + 0.5) << endl; 16 cout << int(15.49 + 0.5) << endl; 15

25. Type Casting • Although the method of type conversion shown above seems simple and effective, the “preferred” method uses the form static_cast<Type>(Expression) • Example double x = 7.2; int ans = 21/static_cast<int>(x)

26. Other Data Types • Single characters may be stored as type char. • Text may be stored as type string. If strings are used in a program, the C++ file must have the preprocessor directive #include<string> • Logical values (true and false) may be stored as type bool (for Boolean).

27. Increment Operators • The increment operator, ++, adds one to the value of an expression. • The effect of the operator is different depending on the location of the operator. int n = 2; int m = 2*(n++); • has the same effect as int n = 2; int m = 2*n; n = n + 1;

28. Increment Operators • The effect of the operator is different depending on the location of the operator. int n = 2; int m = 2*(++n); • has the same effect as int n = 2; n = n + 1; int m = 2*n;

29. Decrement Operators • The increment operator, --, subtracts one to the value of an expression. • The effect of the operator is different depending on the location of the operator. int n = 2; int m = 2*(n--); • has the same effect as int n = 2; int m = 2*n; n = n - 1;

30. Decrement Operators • The effect of the operator is different depending on the location of the operator. int n = 2; int m = 2*(--n); • has the same effect as int n = 2; n = n - 1; int m = 2*n;

31. Types of Errors • Syntax Errors • A violation of the rules of the programming language. • Generally detected by the C++ compiler. • Run-time Errors • An attempt to perform an illegal operation like divide by zero. • Error message at run-time, or error detected by debugging software. • Logic Errors • Computer does exactly what it is told to, unfortunately it is not solving the intended problem. • Programmer must check the result each step in the process until the error is identified.