1. CS111 Lab
Iteration: for loops
Instructor: Michael Gordon

2. for loop structure
 Think of a for loop as a special kind of
while loop with initialization, comparison,
and incrementation built in.
 for (int i = 0; i<n; i++){
instructions…
}

3. Simplest for loops
 The previous slide shows one of the most
common types of for loops.
 Initialize an integer (i) to zero.
 Increment by one (i++)
 As long as i<n (i is less than some number n)
 To count backwards from n, you could do:
 for (int i = n; i<0; i--)
 In addition to incrementing you can do:
 for (int i = n; i<0; i=i+5) etc.

4. When to use for loops
 Use while loops when you don’t know the
number of iterations (such as if the
condition to check depends on the user).
 Use for loops if you know how many times
you need to loop

5. Nested for loops
 You can “nest” one for loop (or more)
inside of another for loop.
 for (int i = 1; i<=2; i++){
for (int j = 1; j<=2; j++){
instructions…
}
}

6. Nested for loops
 The “i” loop runs twice and the “j” loop
runs twice each time the “i“ loop runs.
 for (int i = 1; i<=2; i++){
for (int j = 1; j<=2; j++){
instructions…
}
}
 Make sure to use different variables!