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# Counting and looping

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### Counting and looping

1. 1. Counting and Looping Unit 3 Lecture for Intro to Computer Programming
2. 2. Introduction • Counting in programming can be a very useful tool for, among other things, mathematical calculations. • The primary function for counting in c++ is the for loop. • Loops are used when a process needs to be repeated either a certain number of times, or arbitrarily until a certain set of conditions become true. • The primary looping function (aside from for loops) we will look at is the while loop.
3. 3. For Loops • A for loop is designed to count a given number from one point until it reaches another, every instance running the commands within the loop • The following code is an example of a for loop designed to add consecutive integers, starting at 1 up to a user- inputted number: int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total;
4. 4. For Loops • We’re going to break this down one step at a time, just as a computer would execute it, to see how this loop works. • The very first line initializes an integer variable “total” to equal 0. int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 0
5. 5. For Loops • The second line creates an integer “how_high” and does not initiate it. int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 0 how_high
6. 6. For Loops • Letting the user input how high to count… for this example, let’s say they enter 4. int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 0 how_high = 4
7. 7. For Loops • The for loop begins. Integer j is initialized to = 1 (which is < how_high) and the loop starts. int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 0 how_high = 4 j = 1
8. 8. For Loops • total is increased by j.int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 1 how_high = 4 j = 1
9. 9. For Loops • Then the first iteration of the loop finishes and it returns to the for command… int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 1 how_high = 4 j = 1
10. 10. For Loops • j++ is shorthand for “j = j + 1” so the value for j bumps up to 2, which is still < how_high. int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 1 how_high = 4 j = 2
11. 11. For Loops • total is increased by j.int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 3 how_high = 4 j = 2
12. 12. For Loops • j increases 1. • j < how_high… int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 3 how_high = 4 j = 3
13. 13. For Loops • total is increased by j.int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 6 how_high = 4 j = 3
14. 14. For Loops • j increases 1. • j < how_high… int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 6 how_high = 4 j = 4
15. 15. For Loops • total is increased by j.int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 10 how_high = 4 j = 4
16. 16. For Loops • The next value of j is > how_high, so the for loop ends and continues on in the program, outputting “total = 10” int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; for (int j = 1; j <= how_high; j+ +) { total = total + j; } cout << “total = “ << total; total = 10 how_high = 4 j = 5
17. 17. While Loops • While loops can be much more powerful than a for loop, and can even be made to do the exact same thing, but sometimes it’s a bit more wordy… • The following code is does the same thing as above, only using a while loop: (we won’t go through the step by step of this… if you would like to see it, it is quite easy to write a program to show it to you.) int total = 0; int how_high; cout << “how high would you like to sum?” cin >> how_high; j = 1; do { total = total + j; j = j + 1; } while (j <= how_high) cout << “total = “ << total;