introduction to computer programming

Introduction to Computer Programming

Decisions

If/Else

Booleans

Your old Average friend

import java.util.Scanner;

public class AverageN {

//AverageN - Find the average of N values

public static void main(String[] args) {

Scanner keyb = new Scanner(System.in);

double sum, average, value1, value2, value3;

//get values

System.out.println (“What is value 1?”);

value1 = keyb.nextDouble();





sum = value1 + value2 + value3;

average = sum/3;

System.out.println(“The average is “ + average);

}}

Average Program - did you pass?

• You have the average program averaging 3 grades, but did you pass? If the grade is over 65, you passed.

• How can you code this?

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The if statement

• if statement: Do this only if true

– General syntax:if (<condition>) { <statement> ; ... <statement> ;}

• Example:double average = sum/3;if (average >= 65) { System.out.println(“ You passed.");}

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Relational expressions

Operator Meaning Example Value

== equals 1 + 1 == 2 true

!= does not equal 3.2 != 2.5 true

< less than 10 < 5 false

> greater than 10 > 5 true

<= less than or equal to 126 <= 100 false

>= greater than or equal to 5.0 >= 5.0 true

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if statement flow diagram

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The if/else statement• if/else statement: A Java statement that executes one block of statements if a certain

condition is true, and a second block of statements if it is false.

– General syntax:if (<condition>) { <statement(s)> ;} else { <statement(s)> ;}

• Example: double average = sum/3;

if (average >= 65) { System.out.println(“ You passed.");}

else{ System.out.println(“You failed.”);}

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if/else flow diagram

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if/else question

• Write code to read a number from the user and print whether it is even or odd using an if/else statement.

– Example executions:

Type a number: 42

Your number is even

Type a number: 17

Your number is odd

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Nested if/else statements• nested if/else statement: A chain of if/else that chooses between outcomes using many

conditions.

– General syntax:if (<condition>) { <statement(s)> ;} else if (<condition>) { <statement(s)> ;} else { <statement(s)> ;}

• Example:if (number > 0) { System.out.println("Positive");} else if (number < 0) { System.out.println("Negative");} else { System.out.println("Zero");}

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Nested if/else flow diagram

if (<condition>) { <statement(s)> ;} else if (<condition>) { <statement(s)> ;} else { <statement(s)> ;}

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Nested if/else/if diagram

if (<condition>) { <statement(s)> ;} else if (<condition>) { <statement(s)> ;} else if (<condition>) { <statement(s)> ;}

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Sequential if diagram

if (<condition>) { <statement(s)> ;}if (<condition>) { <statement(s)> ;}if (<condition>) { <statement(s)> ;}

A program to calculate Grade Point Average

Example – Professor Smith gives n tests during the term and uses a grading system, where each test is 1/n of the course grade. Assuming that that the average of the test grades translate into a letter grade as follows:

Test Average Letter Grade 90.0+ A 80-89.9 B 70-79.9 C 60-69.9 D below 60.0 F

write a program that will calculate a student's grade.

A Program To Calculate Test Average

Input - Number of tests and the student's test gradesOutput – Test average and course gradeOther informationA 90+ average is an “A”.A 80-90 average is a “B”.A 70-80 average is a “C”.A 60-70 average is a “D”An average below 60 is an “F”.

Test average = Sum of the test grade/ Number of tests Our first step is to write out our initial algorithm:1. Find the number of tests2. Find the average of n tests3. Find the corresponding letter grade and print it out.

Designing the Grade Program1. Find the number of tests2. Find the average of n tests3. Find the corresponding letter grade and print it out.

1.1 Prompt the user for number of tests1.2 Read the number of tests

Refining the Grade Program1.1 Prompt the user for number of tests1.2 Read the number of tests2. Find the average of n tests3. Find the corresponding letter grade and print it out.

2.1 Add up the test grades2.2 Divide the total by n

Refining the Grade Program1.1 Prompt the user for number of tests1.2 Read the number of tests 2.1 Add up the test grades2.2 Divide the total by n3. Find the corresponding letter grade and print it out.

2.1 For each of the n tests:2.1.1 Prompt the user for the test grade2.1.2 Read the test grade2.1.3 Add it to the total

Refining the Grade Program1.1Prompt the user for number of tests1.2Read the number of tests 2.1For each of the n tests:2.1.1 Prompt the user for the test grade2.1.2 Read the test grade2.1.3 Add it to the total2.2Divide the total by n3. Find the corresponding letter grade and print it out.

System.out.println ("How many tests did you take ?");numTests = keyb.nextInt();

Refining the Grade ProgramSystem.out.println ("How many tests did you take ?");numTests = keyb.nextInt();2.1For each of the n tests:2.1.1 Prompt the user for the test grade2.1.2 Read the test grade2.1.3 Add it to the total2.2Divide the total by n3. Find the corresponding letter grade and print it out.

for (thisTest = 0; thisTest < numTests; thisTest++) {

Refining the Grade ProgramSystem.out.println ("How many tests did you take ?");numTests = keyb.nextInt();for (thisTest = 0; thisTest < numTests; thisTest++) {2.1.1 Prompt the user for the test grade2.1.2 Read the test grade2.1.3 Add it to the total}2.2Divide the total by n3. Find the corresponding letter grade and print it out.

System.out.println ("What grade did you get on this test ?");thisGrade = keyb.nextInt();

Refining the Grade ProgramSystem.out.println ("How many tests did you take ?");numTests = keyb.nextInt();for (thisTest = 0; thisTest < numTests; thisTest++) { System.out.println ("What grade did you get on this test ?"); thisGrade = keyb.nextInt();2.1.3 Add it to the total}2.2Divide the total by n3. Find the corresponding letter grade and print it out.

total = total + thisGrade;

Refining the Grade ProgramSystem.out.println ("How many tests did you take ?");numTests = keyb.nextInt();for (thisTest = 0; thisTest < numTests; thisTest++) { System.out.println ("What grade did you get on this test ?"); thisGrade = keyb.nextInt(); total = total + thisGrade;}2.2Divide the total by n3. Find the corresponding letter grade and print it out.

testAverage = total/numTests;

Refining the Grade ProgramSystem.out.println ("How many tests did you take ?");numTests = keyb.nextInt();for (thisTest = 0; thisTest < numTests; thisTest++) { … … }testAverage = total/numTests; 3. Find the corresponding letter grade and print it out.

3.1 IF Average >= 90 THEN Grade = ‘A’3.2 ELSE IF Average >= 80 THEN Grade = ‘B’3.3 ELSE IF Average >= 70 THEN Grade = ‘C’3.4 ELSE IF Average >= 60 THEN Grade = ‘D’3.2 ELSE Grade = ‘F’

Refining the Grade Program… …testAverage = total/numTests; 3.1 IF Average >= 90 THEN Grade = ‘A’3.2 ELSE IF Average >= 80 THEN Grade = ‘B’3.3 ELSE IF Average >= 70 THEN Grade = ‘C’3.4 ELSE IF Average >= 60 THEN Grade = ‘D’3.2 ELSE Grade = ‘F’

if (testAverage >= 90) courseGrade = 'A';else if (testAverage >= 80) courseGrade = 'B';else if (testAverage >= 70) courseGrade = 'C';else if (testAverage >= 60) courseGrade = 'D';else courseGrade = 'F';

Our program

public static void main(String[] args) { Scanner keyb = new Scanner(System.in); int thisTest, numTests, total, thisGrade; float testAverage; char courseGrade; // Find out the number of classes System.out.println ("How many tests did you take ?"); numTests = keyb.nextInt();

for (thisTest = 0; thisTest < numTests; thisTest++) { System.out.println ("What grade did you get on this test ?"); thisGrade = keyb.nextInt();

// Make sure that the grades are valid // percentages total = total + thisGrade; } // Find the average testAverage = total/numTests; // Find the letter grade corresponding to the // average if (testAverage >= 90) courseGrade = 'A'; else if (testAverage >= 80) courseGrade = 'B'; else if (testAverage >= 70) courseGrade = 'C'; else if (testAverage >= 60) courseGrade = 'D'; else courseGrade = 'F';

// Print the results. System.out.println ("Your test average is " + testAverage); System.out.println ("Your grade will be " + courseGrade); }}

One Last Refinement

• A test score must be between 0 and 100; therefore any grade greater than 100 or else than 0 is invalid.

• Let’s test each grade to make sure it’s valid.

• Also, we have to initialize the total to zero before we do any addition.

The Final Grade Programimport java.util.Scanner;

public class CalcGrade { // Calculates the average test grade and // converts it to a letter grade assuming that // A is a 90 average, B is an 80 average and so // on.that public static void main(String[] args) { Scanner keyb = new Scanner(System.in); int thisTest, numTests, total, thisGrade; float testAverage; char courseGrade; // Find out the number of classes System.out.println ("How many tests did you take ?"); numTests = keyb.nextInt();

//Add up the test grades total = 0; for (thisTest = 0; thisTest < numTests; thisTest++) { System.out.println ("What grade did you get on this test ?"); thisGrade = keyb.nextInt();

// Make sure that the grades are valid // percentages if (thisGrade > 100) System.out.println ("This is not a valid test grade."); else if (thisGrade >= 0) total = total + thisGrade; else System.out.println ("This is not a valid test grade."); }

// Find the average testAverage = total/numTests; // Find the letter grade corresponding to the // average if (testAverage >= 90) courseGrade = 'A'; else if (testAverage >= 80) courseGrade = 'B'; else if (testAverage >= 70) courseGrade = 'C'; else if (testAverage >= 60) courseGrade = 'D'; else courseGrade = 'F';

// Print the results. System.out.println ("Your test average is " + testAverage); System.out.println ("Your grade will be " + courseGrade); }}

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