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

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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;