1. CS149D Elements of Computer Science
Ayman Abdel-Hamid
Department of Computer Science
Old Dominion University
Lecture 20: 11/7/2002
Lecture 20: 11/7/2002
CS149D Fall 2002

2. Outline Looping do-while loop for loop
Break and continue statements within loops
Nested Loops
Lecture 20: 11/7/2002
CS149D Fall 2002

3. The do-while Loop1/2 Condition True ? Execute while Statement(s)
Continue to next
statement No
Yes do
statement;
while (condition); {
statement(s);
}while (condition);
Lecture 20: 11/7/2002
CS149D Fall 2002

4. The do-while Loop2/2 Print 0, 4,16,36,64,100 (0, 22,42,62,82,102)
// while loop solution
int x = 0;
while (x <= 10) {
cout << x*x <<endl;
x +=2; }
//do-while loop solution
int x = 0; do {
cout << x*x <<endl;
x +=2;
} while (x <= 10);
Lecture 20: 11/7/2002
CS149D Fall 2002

5. The for Loop1/2 Execute init statement for (x = 0; x <=10 ; x+=2)
Exit Condition
Execute for_statement(s)
Execute x +=2
Execute next statement
True
False
for (x = 0; x <=10 ; x+=2)
cout << x*x <<endl;
x = 0  init statement
x <=10  Exit condition
x +=2  executed before starting a new iteration
Lecture 20: 11/7/2002
CS149D Fall 2002

6. The for Loop2/2
Print 0, 4,16,36,64,100 (0, 22,42,62,82,102)
// while loop solution
int x = 0;
while (x <= 10) {
cout << x*x <<endl;
x +=2; }
//do-while loop solution
int x = 0; do {
cout << x*x <<endl;
x +=2;
} while (x <= 10);
// for loop solution
int x;
for (x = 0; x <=10 ; x+=2)
cout << x*x <<endl;
Lecture 20: 11/7/2002
CS149D Fall 2002

7. Variations of the for Loop
Init statement, Exit Condition, and expression 2 can all be null
//infinite Loop
for ( ; ; )
cout << “Hi”;
//Equivalent to
while (true)
for ( ; inputVal != -1; )
cin >> inputVal;
//Equivalent to
while (inputVal != -1)
Lecture 20: 11/7/2002
CS149D Fall 2002

8. The break and continue statements1/2
The break statement
Exit immediately from its enclosing loop
The continue statement
Skip any remaining statements in the current iteration, and start a new iteration of the enclosing loop
In while or do-while loop, the condition is evaluated to determine whether or not to start a new iteration
In a for loop, the second expression is executed, then condition is evaluated
Lecture 20: 11/7/2002
CS149D Fall 2002

9. The break and continue statements2/2
// break example
sum = 0;
for (int k=1;k<21;k++) {
cin >>x;
if (x > 10)
break;
sum += x; }
cout << sum;
// continue example
sum = 0;
for (int k=1;k<21;k++) {
cin >>x;
if (x > 10)
continue;
sum += x; }
cout << sum;
Lecture 20: 11/7/2002
CS149D Fall 2002

10. Nested Loops for (i = 1; i <=5; i ++) { for (j = 1; j <=i; j++)
Print the following triangle 1 12
123
1234
12345
for (i = 1; i <=5; i ++) {
for (j = 1; j <=i; j++)
cout << j;
cout <<endl; }
Lecture 20: 11/7/2002
CS149D Fall 2002