Lab-I CSIT-121 Spring 2002

Lab-ICSIT-121 Spring 2002 • Lab Targets • Solving problems on computer • Programming in C++ • Writing and Running Programs • Programming Exercise

Targets • We wish to learn how to program in VC++ • We should know how to launch Visual C++ integrated environment • We should know how to compile a program • Let us work on most fundamental aspects of programming in C++

Programming Fundamentals • We have a real life problem that is to be solved on the computer • In order to solve it, we need to write a program • The program must be written using the syntax rules of Visual C++

Example Problem • A problem is given as follows: • “If a car travels 25 miles per gallon, what is its kilometer per liter rating?” • Given this problem, let us first design a program that will convert miles into kilometers. Thus we can compare the MPG and KPL.

Strategy to solve the problem • How would you solve this problem with paper and pencil? • (Conversion Factor 1 Mile = 1.6 KM)

Solving through programming • We will use C++ syntax to solve this problem on the computer • We first need to know the total number of data items in this problem and their type • TOTAL DATA ITEMS

Solution on paper • Next we should solve it on paper. The solution on paper is called an algorithm • Initial Algorithm • Read the MPG • Convert it to Kilometers per gallon • Convert gallon into liters • Compute Kilometers per liter

Refined Algorithm

How to implement in C++? • How should we implement this solution in C++? • First part is to express the data in C++ • C++ provides data types to capture our real life data into programs • For numbers, we can have whole numbers such as 19 or FP numbers such as 19.63

How to express numbers in C++ • The Kilometers could contain fractional part because of the 1.6 conversion factor • We need a data format that can accept a FP number into it • C++ provides float and double • double dist_km, dist_miles;

Variables and Constants • If you can change the value of a data item in your program, it is known as a variable. • If you cannot change the value of a data item in your program, it is a constant. • Can you change the value of the conversion factor between Miles and Kilometers? • How can we show constant data items?

Constant Data Items • For constant data items, just add the keyword const before their declaration • For example, • const float ConversionFactor=1.6; • (Please notice the “initialization” of the data item with a specific value)

Basic Template to Start a Program • #include <iostream> • using namespace std; • void main() • { • ::: • ::: • ::: • }

Template Description • #include <iostream> • This line tells the system to include pre-defined I/O capability so that we can use the keyboard and screen

Template Description • void main() • This line gives the name of the function that you are developing. main() is the default name used for the main function of any program • Function is a block of code that performs a given task. A function carries a name and opening and closing braces

Program Development Phase-I • In phase-I, we should put our declarations of data items into the template • Let us do it now:

Basic Template to Start a Program • #include <iostream> • using namespace std; • void main() • { • double dist_km,dist_miles; • const float ConversionFactor=1.6; • } • Please note the semicolons after each declaration

Phase-II: Action part • Once we capture our data into data items, we need to perform the actual conversion from miles to kilometers • First we should read the miles from the keyboard • cout<<“Give the distance in miles”; • cin>>dist_miles;

PhaseII: Action part • cout<< is the way to display your data on the screen • cin>>variable_name is the way to read data from the keyboard and assign it to one variable in the program

Q&A • How are fractional numbers (e.g. 3/4 or 1 1/2 are represented in C++? • What is the use of opening braces and closing braces in the program? • What is the difference between variables and constants? • What keyword is added to make a value constant? • What does cin>> do? • Why do we put semicolons at the end of each statement?

Our Program so far…. • #include <iostream> • using namespace std; • void main() • { • double dist_km,dist_miles; • const float ConversionFactor=1.6; • cout<<“Give the distance in miles”; • cin>>dist_miles; • }

Phase II continues • Now we have read the distance in miles • Next, our program should convert it into kilometers using the conversion factor • It is here that we should design an “assignment statement”

Phase II continues • Here, we are multiplying the mileage by the conversion factor and getting the result as distance in km • distance in km = distance in miles*1.6 • This arithmetic expression can be written in C++ using an assignment statement • dist_km = dist_miles*1.6

Rules of Assignment Statement • In C++, you will use the destination variable on left of the equal sign • You cannot use a constant data item on left of the equal sign • You should not assign a FP value to an integer variable • Doing so will cause the loss of fractional part

Programming Exercise • Extend this program by entering the distance traveled in miles from the trip meter. Convert this distance into kilometers and divide by kilometers per liter ratio calculated total fuel consumed in liters. Multiply this quantity by 0.56 to calculate the total amount of money spent in fuel purchase.

Lab-I CSIT-121 Spring 2002