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Exercise Is for (;;;) legal? If so, what does it mean?

Exercise Modify the program so that the square root is computed only once.

Continue statements

Concept The break statement is used to exit a loop from an arbitrary location in its body; the continue statement is used to skip the rest of a loop body and return to evaluate the condition for continuing the loop.

Program: Control08.java

// Learning Object Control08 //    continue statementspublic class Control08 {     static final int N = 10;    public static void main(/*String[] args*/) {        int sum = 0;         for (int i = 0; i < N; i++) {             if (i % 2 == 0) {                if (i % 3 == 0)                     continue;                else                     sum = sum + i;            }             else if (i % 3 == 0)                sum = sum + i;             else                continue;         }        System.out.println(sum);     }}

This program sums all the positive integers less than N that are divisible by 2 or 3 but not by both. For N=10 , the result is 2 + 3 + 4 + 8 + 9 = 26 .

  • The constant N and the variable sum are allocated and initialized.
  • The for loop is standard and is executed for the values 0 through N - 1 .
  • If i is divisible by 2 and also by 3 (for example, 6), the continue statement is executed and the variable sum is not modified.
  • If i is divisible neither by 2 nor by 3 (for example, 5), the continue statement is executed and the variable sum is not modified.
  • In all other cases, the value of i is added to sum .
  • The final value of sum is printed.

Exercise Modify the program so that it explicitly checks for divisibility by 6, instead of checking for divisibility by 2 and 3 inseparate statements.

Exercise Modify the program so that continue is not used.

Switch statements

Concept A switch statement is a generalization of an if statement. Instead of selecting between two alternatives depending on the valueof a boolean-valued expression, an integer-valued expression is used and there can be multiple alternatives introduced by the keyword case . Since there are a very large number ofinteger values, an alternative labeled default is executed when the value in the expression is not explicitly listed in one of the alternatives.

Important: In an if -statement, the end of the statement (or block of statements) of the first alternative causes a transfer of controlto the end of the if statement, skipping over the statement (or block of statements) in the second ( else ) alternative. This does not happen in a switch : control “drops through” from the end of one alternative to the beginning of the next alternative.A break statement must be used to transfer control from the end of an alternative to the end of the switch statement.

Program: Control09.java

// Learning Object Control09 //    switch statementspublic class Control09 {     public static void main(/*String[] args*/) {         int year = 2001;        int month = 4;         int days;        switch (month) {             case 2:                days = (year % 4 == 0) ? 28 : 29;                 break;            case 4:             case 6:            case 9:             case 11:                days = 30;             default:                days = 31;         }        System.out.println(days);     }}

This program computes the number of days in a month.

  • The variables are allocated and the first two, year and month , are given initial values.
  • The switch statement chooses a case depending on the value of the variable month . Jeliot displays Entering a switch statement .
  • The case associated with 4 is selected. Jeliot displays This case is selected . The assignment statement assigns 30 to days .
  • The assignment statement assigns 31 to days .
  • The switch statement terminates and Jeliot displays Exiting a switch statement .
  • The value of days is printed.

Exercise Explain why the second assignment statement is executed; fix the program.

Exercise Explain why the sequence of case 's for 4 , 6 , 9 , 11 works.

Exercise Modify the program so that the case 's for the 31-day months are given explicitly and so that the days are computed correctly in leap years.

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In biology, a pathogen (Greek: πάθος pathos "suffering", "passion" and -γενής -genēs "producer of") in the oldest and broadest sense, is anything that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term pathogen came into use in the 1880s.[1][2
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Source:  OpenStax, Learning objects for java (with jeliot). OpenStax CNX. Dec 28, 2009 Download for free at http://cnx.org/content/col10915/1.2
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