Section 05: Loops

Question 1

What is a recursive function?

Answer 1

Function that calls itself

Question 2

Define

Tracing

Answer 2

Way of representing how program will work each step of the way

Question 3

How can a while loop be used for input validation?

Answer 3

• Want to check for the validity of the data received

General Algorithm:

1. Ask user for some data
2. Check if its valid
3. As long as data is invalid → go back to step 1; otherwise, continue w program

Therefore, while loop useful

Question 4

Structure

If statement:

Answer 4

if condition : instructions

Indented block of code is executed once, only if condition evluates true

Question 5

Define and structure

for loop

Answer 5

for variable in sequence: instructions

*Indented block of code executed repeatedly, once for each element in a sequence*

• First iteration: variable assigned the value of the first element in sequence
• Successive Iteration: variable assigned value next element

Question 6

Define

Range function

Answer 6

Rather than predefining sequence of values → range function

• range(n) gives sequence for numbers 0, 1, … n

• range(start, n) produces sequence from start to n -1
• range(start, n, step) produces sequence from start to n-1 with gap of step variable

Question 7

What is the relation between for loops and while loops?

Answer 7

Always replace while loops with a for loop and visa versa

Generally …

1. While loop when the number of iteraiton is not known ahead of time
2. for loop when num of iterations is fixed OR want to preform same operation on all elements of a sequence

Question 8

Define

What is variable scope?

Answer 8

• Innermost possible scope: Function Body
• therefore, Variable created inside body of a loop/conditional statement → variable can be accessed later = assuming the body was executed at least once

Question 9

Define

Break and Continue statements in loops:

Answer 9

Break statement cause program to exit the current loop

Continue statement cause program to skip to next iteration

Give more control over loop execuation → make code more difficult to read and debug

Question 10

Compare

When to use recursive vs. loop functions?

Answer 10

Chose based off of complexity and memory (size of code)

1. Aim for time efficiency and if num of recursive calls is large ⇒ use iteration
2. Aim efficiency is not an issue and having a shorter code important ⇒ use recursion

Recursion is when a function calls itself within its code, thus repeatedly executing the instructions present inside it.

Iteration is when a loop repeatedly executes the set of instructions like “for” loops and “while” loops.

Question 11

Define

Control flow determines …

Answer 11

Control flow determines …

1. Which part of code should be executed
2. Which parts of code should be executed only under certain circumstances
3. Which parts of the code should be executed repeatedly

Control flow is not fixed and can change during execution

Question 12

Structure

Structure of a while loops:

Answer 12

while condition:
instruction 1
instruction 2
etc …

Repeatedly executed as long as condition evaluates as True

Question 13

Defne

Iterations:

Answer 13

Iternation: single execution of the instructions in the body of the loop (#num of repetitions)

• Variable acts as loop counter
• No upper limit to iternations: infinite loop

Question 14

Compare

If statement vs. while loop

Answer 14

If Statement:
* Conditions checked once (before executing body)
* Block of code is executed at most once, if condition evaluates as true

While Loop:
* Conditions checked once per iternation of the loop
* Block of code is executed repeatedly, as long as condition evaluates as true