Advanced Computer Programming

Transcription

1 Hazırlayan Yard. Doç. Dr. Mehmet Fidan

2 WHILE, DO-WHILE and FOR LOOPS Loops are used for executing code blocks repeatedly. Decision of continuing loop is given by boolean expression. If boolean expression is false, then the code block is not executed. For loops repeats the execution of code blocks in a certain number. Count controlled loop. while and do-while loops repeats code execution in an unknown number of iterations. Condition controlled loop.

3 WHILE, DO-WHILE and FOR LOOPS In for and while loops, logical expressions are tested first. If expression is true then the code block inside the loop is executed, else program doesn t enter the loop. In do-while loops code block is executed without checking boolean expression result for once. Then before second iteration boolean expression result is checked, and loop continuation is decided.

4 WHILE LOOP Two types of uses: while (logical expression is true) statement; while (logical expression is true) statement; statement;

5 WHILE LOOP Example:

6 DO-WHILE LOOP do statement; while(logical expression is true); do statement; statement; while(logical expression is true) ;

7 DO-WHILE LOOP Example:

8 FOR LOOP for( initialization; logical expr.(termination); increment) statement; initialization expressions are executed once before loop starts. If there are multiple initialization expressions, they are separated with a comma ",". increment,expression are executed after each iteration If there are multiple increment expressions, they are separated with a comma ",". Execution order is from left to right. After increment operations, logical expression is evaluated and loop terminates if logical expression is false. Else loop enters next iteration.

9 FOR LOOP for (expression1 ; expression2 ; expresion3) statements; expression1, executed once before for loop starts. It could be one or multiple mathematical or other operations.

10 FOR LOOP for (expresion1 ; expression2 ; expresion3) statements; expression2, is a logical operation that returns true or false result. It is not a requirement that expression2 includes variables used in expression1.

11 FOR LOOP for (expression1; expression2; expression3) statements ; expression3, usually changes result of expression2, but it is not a necessity. It is executed after each iteration.

12 FOR LOOP Example: for (int counter = 1; counter <= 10; counter ++) Console.WriteLine(counter.ToString());

13 FOR LOOP Example: int counter = 1; for ( ; counter <= 10; ) Console.WriteLine(counter.ToString()); counter ++; int counter = 1; for ( ; ; ) Console.WriteLine(counter.ToString()); counter ++; if (counter >10) break;

14 FOR LOOP Notes: expression1, expression2, and expression3 within the for loop could be empty but, we must use semi colons. If epression1 and epression3 are not used, for loop behaves like while loop. We can not know when will the loop terminated if expression2 is not used. In this case loop can be terminated by break expression. expression1 and expression3 might include more than one expressions. The intention of this type of usage is simplifying program code.

15 FOR <-> WHILE expression1; while (expression2) statements; expression3; Exactly the same operations. for (expression1; expression2; expression3) statements;

16 FOR <-> WHILE Example: int counter; for(counter = 0; counter <= 10; counter++) Console.WriteLine( The value of counter : + counter); int counter; counter = 1 ; while (counter <= 10 ) Console.WriteLine( The value of counter : + counter); counter++ ;

17 Example: FOR LOOP static void main ( ) int k, n ; for( k = 1, n = 12 ; k<9 && n>6 ; k++, n--) Console.WriteLine ("k= + k + n= + n) ; There can be multiple expressions separated with commas. There can be multiple expressions separated with commas.

18 EXERCISE Write a game that generates a random number between 0 and 100 which user will try to guess the number. After user enters a number, program will reply to the user that, his/her guess is bigger or smaller that the generated number. If user writes the correct answer, program will congratulate user and exit.

19 Algorithm: EXERCISE number = pick a random number bettween 0 and 100 while(true) print Make a guess" read guess if (guess is equal to the number) break loop else if(guess is smaller than number) print smaller else print bigger

20 EXERCISE Solution:

21 BREAKING the LOOP break keyword is used to terminate the loop. If there are nested loops break terminates only the inner loop. continue keyword skips current iteration and jumps to next one. Both keyword are heavily used in the implementation of the algorithms.

22 break; TERMINATING LOOP The loop seen below terminates when variable x takes the value of 5. int x = 0; for( ; ; ) /* infinite loop */ if(x == 5) break; Console.WriteLine(x.ToString()); x++;

23 continue; RESUMING NEXT LOOP ITERATION The code section seen below prints the numbers between 0 and 9 except for 5. int x; for( x = 0; x < 10 ; x++) if(x == 5) continue; Console.WriteLine( X = + x);

24 continue; RESUMING NEXT LOOP ITERATION for( x = 0; x < 10 ; x++) if(x == 5) continue; Console.WriteLine(x.ToString()); Both codes produces same results. for( x = 0; x < 10 ; x++) if(x!= 5) Console.WriteLine(x.ToString());

25 EXAMPLE: NESTED FOR LOOPS