loop - Programming Summary of Loops Prog Fundamentals I:...

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Unformatted text preview: Programming Summary of Loops Prog Fundamentals I: Summary of Loops /Slide 2 Which Loop to Use? q for loop s s q while loop s s s 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 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. 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. q do-while loop s s Prog Fundamentals I: Summary of Loops /Slide 3 How to Stop a Loop q 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. q q Prog Fundamentals I: Summary of Loops /Slide 4 break q break is used when we want to terminate a loop before it ends in a normal way. How it works: s When the break statement is executed, the loop statement terminates immediately. s The execution continues with the statement following the loop statement. q Prog Fundamentals I: Summary of Loops /Slide 5 Maximum (while with break) int value=0; int max=0; while(true) { // input value // maximum value // 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; Prog Fundamentals I: Summary of Loops /Slide 6 Common Loop Errors while(balance != 0.0); { balance = balance - amount; } s This will lead to an infinite loop! for(count=1; count<=number; count+ +); { cout << "hello" << endl; } Prog Fundamentals I: Summary of Loops /Slide 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; } Prog Fundamentals I: Summary of Loops /Slide 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; } s s Be sure to initialize to 0 a variable used for sums. Be sure to initialize to 1 a variable used for products. Prog Fundamentals I: Summary of Loops /Slide 9 Nested Loops q q Nested loops are loops within loops. Nested loops are similar in principle to nested if and if-else statements. Many applications require nested loops. q Prog Fundamentals I: Summary of Loops /Slide 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'); Prog Fundamentals I: Summary of Loops /Slide 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; } Prog Fundamentals I: Summary of Loops /Slide 12 Zig Zag Pattern q Print out the following ZigZag pattern *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** Prog Fundamentals I: Summary of Loops /Slide 13 Zig Zag Pattern q Sub-problem: print out the upper part s print out the middle part s print out the lower part s q Print out upper part: s s s s s 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; 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; Row 10 - 14 repeat the upper part *** *** *** *** *** *** *** *** *** *** q Print out middle part: s s s s s q Print out lower part: s Prog Fundamentals I: Summary of Loops /Slide 14 Zig Zag Pattern q Algorithm for upper part: s s s s s row 0: print ( 5-row%5 )spaces, 3 stars; row 1: print ( 5-row%5 )spaces, 3 stars; row 2: print ( 5-row%5 )spaces, 3 stars; row 3: print ( 5-row%5 )spaces, 3 stars; row 4: print ( 5-row%5 )spaces, 3 stars; *** *** *** *** *** q Algorithm for middle part: s s s s s row 5: print ( row%5 )spaces, 3 stars; row 6: print ( row%5 )spaces, 3 stars; row 7: print ( row%5 )spaces, 3 stars; row 8: print ( row%5 )spaces, 3 stars; row 9: print ( row%5 )spaces, 3 stars; *** *** *** *** *** q Algorithm for lower part: s Row 10 - 14: print (5-row%5 ) space, 3 stars; Prog Fundamentals I: Summary of Loops /Slide 15 Zig Zag Pattern #include <iostream.h> 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 % 5; else space = row % 5; //row 5 ~ 9, 15 ~ 19 , … for ( k = space; k > 0; k--) cout << " "; cout << "***" << endl; } return 0; } //print initial spaces ...
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This note was uploaded on 09/30/2010 for the course COMP COMP102 taught by Professor Lrr during the Fall '09 term at HKUST.

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