8.5 Repetition with Loop Until

8.5 Repetition with Loop Until

The loop-until construct is similar to the while loop. The main difference is that in the loop-until, the condition is evaluated after the repeat group. This means that the operations in the repeat group, Block1, will be carried out until the condition is true. Figure 8.3 shows a portion of the flowchart for the loop-until construct.

Figure 8.3: Flowchart segment for the loop-until construct.

Note

Independent of the initial evaluation of the condition, the operations in the loop will be carried out at least once. If the condition is true, the operations in the repeat group will be carried out only once.

The KJP code for the loop-until construct is written with the repeat compound statement, which uses the keywords repeat, until, and endrepeat. The repeat group consists of all operations after the repeat keyword and before the until keyword.

The general concepts of loop counters and loop conditions also apply to the loop-until construct. The following portion of code shows the general structure for the loop-until statement.

             repeat                〈 statements in Block1 〉             until 〈 condition 〉             endrepeat 

As a simple example, consider a mathematical problem of calculating the summation of a series of integer numbers. These start with some given initial number, with the constraint that the total number of values added is below the maximum number of values given; for example, the summation of integer numbers starting with 10 in increments of 5 for a total of 2000 numbers. For this problem, a counter variable, numbers, is used to store how many of these numbers are counted. An accumulator variable is used for storing the value of the intermediate sums. Every time through the loop, the value of the increment is added to the accumulator variable called sum.

Class Sum computes the summation of a series of numbers. The KJP implementation of this class follows.

On the CD

The KJP code that implements class Sum is stored in the file Sum.kpl.

       description          This class calculates summation for a series of          numbers.   */       class Sum is         public         description            This is the main function in the program.  */         function main is          variables             integer sum       // accumulates summations             integer numbers   // number of values to sum             integer svalue    // starting value             integer maxnum    // maximum number of values             integer inc_value // increment value          begin                // body of function starts            display "Enter starting value: "            read svalue            display "Enter number of values: "            read maxnum            display "Enter increment: "            read inc_value            set sum = svalue            set numbers = 0            repeat               add inc_value to sum               increment numbers            until numbers >= maxnum            endrepeat            display "Summation is: ", sum, " for ",                      numbers, " values"          endfun main       endclass Sum 

On the CD

The code for the Java implementation of class Sum follows. This code is stored in the file Sum.java and was generated by the KJP translator.

       // KJP v 1.1 File: Sum.java, Fri Dec 06 14:23:54 2002       /** This class calculates summation for a series of          numbers.   */       public  class Sum {         /** This is the main function in the program.   */         public static void main(String[] args) {            // data declarations            int  sum;       // accumulates summations            int  numbers;   // number of values to sum            int  svalue;    // starting value            int  maxnum;    // maximum number of values            int  inc_value; // increment value            // body of function starts here            System.out.println("Enter starting value: ");            svalue = Conio.input_Int();            System.out.println("Enter number of values: ");            maxnum = Conio.input_Int();            System.out.println("Enter increment: ");            inc_value = Conio.input_Int();            sum =  svalue;            numbers =  0;            do {                sum += inc_value;                numbers++;            } while (!( numbers >= maxnum) );            System.out.println("Summation is: "+ sum+                 " for "+ numbers+ " values");         }  // end main       }  // end Sum 

The execution of this program with the indicated input values is shown in Figure 8.4.

Figure 8.4: Execution of program with class Sum.