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Counting and looping

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Counting and looping Counting and looping Presentation Transcript

  • Counting and Looping Unit 3 Lecture for Intro to Computer Programming
  • 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.
  • 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;
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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;