Week 6 of the course

Self-study¶

The topics for this week are the following: (i) STL algorithms (ii) Lambda functions and (iii) Tuning STL algorithms and containers

The following links will take you to the video-lectures and the accompanying slides:

STL algorithms

STL algorithm - examples

Lambda functions

Lambda functions and capturing variables

Tuning STL algorithms and containers

Ordinary slides from all lectures

STL algorithms - examples: c++ code

STL algorithms¶

Question 1

Suppose one has some STL container in variable \(A\) and one wishes to input \(A\) into an STL algorithm \(X\). What parameter (or parameters) would one input to \(X\) to indicate that one wishes \(X\) to use the entire container \(A\)?

One need input simply the variable \(A\).

One must input the actual values of the first and last elements of \(A\).

An iterator to the beginning of \(A\) and an iterator to the end of \(A\).

One must input the variable \(A\) along with the container type (for example vector, list, map).

Question 2

For what reasons is it better to use algorithms from the STL library to compute some task rather than writing your own algorithms for computing the task? (There may be more than 1 correct reason.)

Using STL algorithms makes code more readable and understandable.

An STL algorithm always has better runtime efficiency than corresponding code that you write yourself.

In an STL algorithm special cases and potetial error situations are handled.

When using an STL algorithm, you do not have to know or understand what you are computing.

STL algorithms - examples¶

Question 1

Suppose begin and end are two iterators associated with vector v. Suppose the location to the right of begin is \(i\) and the location to the right of end is \(j\). What is the significance of the difference end - begin?

The difference is a new iterator where end is shifted \(i\) locations to the left.

The difference is the numerical value of \(j-i\).

The difference is the numerical value of \(j-i + 1\).

The difference is the numerical value of \(i-j + 1\)..

Question 2

Which of the following is true about the STL algorithsm?

They are building blocks which one can use in forming one’s own algorithm to compute one’s own task.

There is an STL algorithm available which will solve any computational task one will ever encounter.

They are useless because the tasks they handle are too simple.

Lambda functions¶

Lambda functions and variable captures¶

Question 1

When we say a lambda function captures a variable we mean

that it will be impossible for any other function, other than the lambda function, to use a variable having the same name as the captured variable

that the lambda function deletes a local variable from the calling function

that the lambda function makes a copy of a variable or a reference that it uses inside itself

that when the lambda function uses a local variable, the variable name must begin with the prefix capt!, which is an abbreviation for captured

Question 2

Suppose in C++ one has a vector v of integers and d is some nonzero integer. What will be the value of a when the following is executed?:: int a = std::count_if(v.begin(), v.end(), [d](int i){return (i % d != 0 && i*d > 0 );});

The number of nonzero elements in v that are greater than d.

Zero always.

The number of elements in v that are divisble by d or have the same sign as d.

The number of elements in v that are not divisble by d and have the same sign as d.

Tuning STL algorithms and containers¶

Question 1

Which of the following statements, regarding tuning of STL algorithms, is true? (More than one statement may be true.)

By using tuning, we can expand the use of existing STL algorithms.

When an STL algorithm is tuned, the number of parameters input to the algorithm always increases.

To tune an STL algorithm we must actually rewrite the STL algorithm code to meet our requirements.

When tuning an STL algorithm we rename the STL algorithm to clarify its use in our code.

When tuning an STL algorithm we often add a named function or a lambda function to an STL algorithm call.

Question 2

The STL contains algorithms named count_if, find_if and remove_if. Which of the following properties do all these algorithms have?

They all require precisely two input parameters, which are both iterators.

One of the parameters they require is either a lambda function or a pointer to a named function.

All of the them return one iterator.

The iterators used as input parameters cannot be associated with a vector container.

Extra links on the topic:

STL algorithms from cppreference.com

Week06 - Glossary

Homework to be returned for the weekly exercises¶

Questions to be submitted this week

Week 6 of the course¶

Self-study¶

STL algorithms¶

STL algorithms - examples¶

Lambda functions¶

Lambda functions and variable captures¶

Tuning STL algorithms and containers¶

Homework to be returned for the weekly exercises¶