Chapter 3. Expressions and Interactivity

1. Chapter 3. Expressions and Interactivity Csc 125 Introduction to C++

2. Type Conversion • Operations are performed between operands of the same type. • If not of the same type, C++ will convert one to be the type of the other • This can impact the results of calculations.

3. Data type ranking

4. Type coercion • Type Coercion: automatic conversion of an operand to another data type • Promotion: convert to a higher type • Demotion: convert to a lower type

5. Type coercion • char, short, unsigned short automatically promoted to int • When operating on values of different data types, the lower one is promoted to the type of the higher one. • When using the = operator, the type of expression on right will be converted to type of variable on left

6. Overflow and Underflow • When a variable is assigned a value that is too large or too small in range for that variable’s data type, the variable overflows or underflows. • Variable contains value that is ‘wrapped around’ set of possible values • No warning or error message is given, if an overflow or underflow occurs, the program will use the incorrect number, and therefore produce incorrect results

7. Type casting • Manual data type conversion • The general format of a type cast expression • static_cast<DataType> (Value) • Example double number=4.6; int val; val=static_cast<int> (number)

8. Type casting int months, books; double perMonth; perMonth=static_cast<double>(books)/months perMonth=static_cast<double>(books/months)

9. Type casting (Another Example) void main() { int number=99; cout<<number<<endl; cout<<static_cast<char>(number)<<endl; }

10. Named constant • For example, assume that the tuition rate is $128 per credit hour. Compute monthly payment for Peter’s tuition and display the amount he needs to pay.

11. Named constant void main() { float tuition,payment; int creditHours; count<<“How many credit hours you\’ll take in spring? ”; cin>>creditHours; tuition=creditHours*128; cout<<“Monthly payment= ”<<tuition/5<<endl; count<<“How many credit hours you\’ll take in Fall? ”; cin>>creditHours; tuition=creditHours*128; cout<<“Monthly payment= ”<< tuition/4 <<endl; }

12. Named constant • A named constant is really a variable whose content is ready-only, and cannot be changed while the program is running • const double TUITION_RATE=128;

13. Named constant void main() { float tuition,payment; int creditHours; const short tuitionRate=128; count<<“How many credit hours you\’ll take in spring? ”; cin>>creditHours; tuition=creditHours*?; cout<<“Monthly payment= ”<<tuition/?<<endl; count<<“How many credit hours you\’ll take in Fall? ”; cin>>creditHours; tuition=creditHours*?; cout<<“Monthly payment= ”<< tuition/? <<endl; }

14. Named constant • To define common value that is difficult to remember, const double PI=3.1415926; • To indicate that array’s size. Here is an example const int SIZE=21; char name[SIZE];

15. Multiple assignment • Multiple assignment means to assign the same value to several variable with one statement. • int a, b, c,d; • a=b=c=d=12;

16. Combined assignment operators • Assume x=10; x=x+4; x=x-2; x=x*10; x=x/5; x=x%4;

17. combined assignment operators • C++ provides a special set of operators designed specifically for these jobs • Compound operators

18. More examples result*=a+5;