Programming

1. Programming Summary of Loops

2. Which Loop to Use? • for loop • for calculations that are repeated a fixed number of times • controlled by a variable that is changed by an equal amount (usually 1) during each iteration • while loop • The number of iterations depends on a condition which could be changed during execution. • Example: working with user input. • In some situations the code segment should not be executed at all. • do-while loop • The code segment is always executed at least once. • Otherwise, the situations when do-while loops are used are very similar to those when while loops are used.

3. How to Stop a Loop • Known number of iterations before the loop stops (for). • Test for a user-controlled condition before or after each iteration (while, do-while). • Use the break command.

4. break • break is used when we want to terminate a loop before it ends in a normal way. • How it works: • When the break statement is executed, the loop statement terminates immediately. • The execution continues with the statement following the loop statement.

5. Maximum (while with break) int value=0; // input value int max=0; // maximum value while(true) // infinite loop!!! { cout << "Enter a positive integer " << "(-1 to stop):"; cin >> value; if(value > max) max = value; if(value==-1) break; } cout << "The maximum value found is " << max << endl; MAX

6. Common Loop Errors while(balance != 0.0); { balance = balance - amount; } • This will lead to an infinite loop! for(count=1; count<=number; count++); { cout << "hello" << endl; } • "hello" only printed once!

7. Common Loop Errors double balance = 333.3; double amount = 33.33; int round=0; char tmp; while(balance != 0.0){ balance = balance - amount; cout << round++ <<": the balance is " << balance <<endl; cin >> tmp; } • balance may not become equal zero due to numerical inaccuracies.

8. Common Loop Errors int power = 0, n; cout << "Give N :"; cin >> n; while(power <= 1000){ cout <<"Next power of N is ” << power << endl; power *= n; } • Be sure to initialize to 0 a variable used for sums. • Be sure to initialize to 1 a variable used for products.

9. Nested Loops • Nested loops are loops within loops. • Nested loops are similar in principle to nested ifand if-else statements. • Many applications require nested loops.

10. Nested Loops // Find the average score on 8 lab assignments int counter, lastlab=8; double avg, score, tscore; char resp; do{ tscore = 0; for(counter =1; counter <=lastlab; counter ++){ cout << "Enter student’s score for lab " << counter << ": "; cin >> score; tscore += score; } avg = tscore/double(lastlab); cout << "The average score is " << avg << endl; cout << "Enter another student (y/n)? "; cin >> resp; }while(resp=='y' || resp=='Y');

11. Multiplication Table // Program to output the // multiplication table int row; // Outer loop counter int col; // Inner loop counter for(row=1; row<=10; row++){ for(col=1; col<=10; col++) cout << row*col << " "; cout << endl; }

12. Zig Zag Pattern • Print out the following ZigZag pattern * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

13. Zig Zag Pattern • Sub-problem: • print out the upper part • print out the middle part • print out the lower part • Print out upper part: • row 0: print 5 spaces, 3 stars; * * * • row 1: print 4 spaces, 3 stars; * * * • row 2: print 3 spaces, 3 stars; * * * • row 3: print 2 spaces, 3 stars; * * * • row 4: print 1 space, 3 stars; * * * • Print out middle part: • row 5: print 0 space, 3 stars; * * * • row 6: print 1 space, 3 stars; * * * • row 7: print 2 spaces, 3 stars; * * * • row 8: print 3 spaces, 3 stars; * * * • row 9: print 4 spaces, 3 stars; * * * • Print out lower part: • Row 10 - 14 repeat the upper part

14. Zig Zag Pattern • Algorithm for upper part: • row 0: print ( 5-row%10 )spaces, 3 stars; * * * • row 1: print ( 5-row%10 )spaces, 3 stars; * * * • row 2: print ( 5-row%10 )spaces, 3 stars; * * * • row 3: print ( 5-row%10 )spaces, 3 stars; * * * • row 4: print ( 5-row%10 )spaces, 3 stars; * * * • Algorithm for middle part: • row 5: print ( row%10 - 5 )spaces, 3 stars; * * * • row 6: print ( row%10 - 5 )spaces, 3 stars; * * * • row 7: print ( row%10 - 5)spaces, 3 stars; * * * • row 8: print ( row%10 - 5)spaces, 3 stars; * * * • row 9: print ( row%10 - 5 )spaces, 3 stars; * * * • Algorithm for lower part: • Row 10 - 14: print (5-row%10 ) space, 3 stars;

15. Zig Zag Pattern #include <iostream> using namespace std; int main() { int space,row,k,j ; for(row = 0; row < 15; row++) { if ( row%10 – 4 <= 0 ) //row 0 ~ 4, 10 ~ 14 , … space = 5 - row % 10; else space = row % 10 - 5; //row 5 ~ 9, 15 ~ 19 , … for ( k = space; k > 0; k--) //print initial spaces cout << " "; cout << "***" << endl; } return 0; }