1. for & do/while Loops

2. Purpose: Improved syntax for Counter-Controlled Loops
for loops
Purpose: Improved syntax for Counter-Controlled Loops

3. for loops
c = start; // could be many lines while (c <= stop) { c += increment; }

4. for loops Syntax: for (initStmt; condExpr; incStmt) body Where:
- body is a single statement with a
semicolon, or a Block { } .

5. for loops Semantics: for (initStmt; condExpr; incStmt) body
1. Execute initStmt;
2. When condExpr is FALSE, skip the body.
When condExpr is TRUE:
Execute the body
Execute the incStmt
Repeat step 2.

6. for loops
Style:
for (initStmt; condExpr; incStmt)
oneStatement ; { }

7. for loops Example 1: (warning: poor style!) int i;
for (i=2; i<=12; i+=2)
cout << i << ” ”;
cout << ”\ni =” << i;
Prints:
i = 14

8. for loops Example 1: (style corrected) int i;
for (i=2; i<=12; i+=2)
cout << i << ” ”;
cout << ”\ni =” << i;
Prints:
i = 14

9. for loops Example 2: counting backwards for (i=10; i>=1; i--) {
cout << i << ” ”; }
cout << ”\ni =” << i;
Prints:
i = 0

10. for loops Example 3: zero iterations for (i=10; i<=5; i++) {
cout << i << ” ”; }
cout << ”\ni =” << i;
Prints:
i = 10

11. for loops Example 4: sum all numbers 2 to 10 int i, sum = 0;
for (i=2; i<=10; i++) {
sum = sum + i; }
cout << sum;
Prints: 54

12. for loops
Alternate Control Variable Declaration: int i; for (i=1; i<=10; i++) { } Can be written as: for (int i=1; i<=10; i++) { // but i is undefined after the loop

13. for loops
Nested for loops: Prints: for (int i=1; i<=3; i++) 1 5 for (int j=5; j<=7; j++) 1 6 cout << i << ” ” 1 7 << j << endl;

14. do/while loops
Purpose: Same as a while loop, except the condition is checked at the bottom instead of the top. Use when: there should be at lease one iteration.

15. do/while loops Syntax: do body while (condExpr); Where:
- body is a single statement with a
semicolon, or a Block { } .

16. do/while loops Semantics: do body while (condExpr);
1. Execute the body
2. When the condExpr is TRUE, repeat step 1
When the condExpr is FALSE, skip body

17. do/while loops
Style 1: do
oneStatement;
while (condExpr);

18. do/while loops
Style 2: common
do {
statements
} while (condExpr);

19. do/while loops Style 3: less common do { oneStatement; }
while (condExpr);

20. do/while loops Example 1: validation loop int n; do {
cout << ”Enter negative number: ”;
cin >> n;
if (n >= 0)
cout << ”Try again!\n”;
} while (n >= 0);

21. do/while loops Example 2: menu loop string option; do {
// print menu, with X=exit
cout << ”Enter menu option: ”;
cin >> option;
// switch or nested if/else’s
} while (option != ”X”);