Understanding For Loops in C++: Syntax, Initialization, and Examples

1. Programming for Loops

2. The for Statement initialization condition false true action update

3. The for Statement • Syntax for (initialization; condition; update) action • How it works: • execute initialization statement • while condition is true • execute action • execute update • Example: int i; for(i=1; i<=20; i++) cout << "i is " << i << endl;

4. N! int number, factorial, n; cout << "Enter positive integer:"; cin >> number; factorial = 1; for(n=1; n<=number; n++) factorial *= n; cout << "The factorial of " << number << " is " << factorial << endl;

5. 2N int number, result, n; cout << "Enter positive integer:"; cin >> number; result = 1; for(n=1; n<=number; n++) result *= 2; cout << "Two raised to the " << number << " power is " << result << endl;

6. int main() {int listSize, n;int value;double sum = 0;double average; cout << "How many input numbers? " << endl; cin >> listSize; cout << " Please enter the " << listSize << " input numbers: " << endl; for (n=listSize; n > 0; n--) { cin >> value; sum += value; } if (listSize >0) { average = sum / listSize; cout << "Average: " << average << endl; }return 0;}

7. Loops (Iteration) • Make sure there is a statement that will eventually stop the loop. • INFINITE LOOP == loop that never stops • Make sure to initialize loop counters correctly. • OFF-BY-ONE == the number of times that a loop is executed is one too many or one too few. • Have a clear purpose for the loop.

8. Increment and Decrement • C++ has special operators for incrementing (++) and decrementing (--) an integer by one. • The ++ operator functions as follows: • ++k: increments the value of k by one and the incremented value is used in the expression. • Example: int k = 1, j; j =++k;//First: k increased by 1, becomes 2, // Second: j is assigned to 2k = 3;cout << ++k; // First: k is increased by 1, becomes 4, // Second: 4 outputs to the screen

9. Increment and Decrement k++ uses the initial value of k in the expression and increments afterwards. Example: int k = 1, j; j = k++; // First: j is assigned to 1 //Second: k is increased by 1, becomes 2 k = 3; cout << k++; //First:3 printed on the screen // Second:k is increased by 1, becomes 4,

10. Increment and Decrement The -- operator functions as follows: • --k decrements the value of k by one and the decremented value is used in the expression. Example: int k = 1, j; j =--k; // First: k decreased by 1, become 0, // Second: j is assigned to 0 k = 3; cout << --k; // First: k is decreased by 1, becomes 2, // Second: 2 is output to the screen

11. Increment and Decrement k-- uses the initial value of k in the expression and decrements afterwards. Example: int k = 1, j; j = k--; // first: j is assigned to 1 // second: k decreased by 1, becomes 0, k = 3; cout << k--; //First: 3 output to the screen //Second: k is decreased by 1, becomes 2

12. Increment and Decrement • Examples: int k = 4; cout << k << endl;cout << ++k << endl; // k=k+1 : k is 5 cout << k++ << endl; // k=k+1 : k is 6 int i = k++; // i is 6, k is 7cout << i << " " << k << endl; int j = ++k; // j is 8, k is 8cout << j << " " << k << endl;

13. Increment and Decrement • Examples: int k = 4; cout << k << endl;cout << --k << endl; // k=k-1 : k is 3 cout << k-- << endl; // k=k-1 : k is 2 int i = k--; // i is 2, k is 1cout << i << " " << k << endl; int j = --k; // j is 0, k is 0cout << j << " " << k << endl;