TCPP2 Functions

Section 6.7 Functions

In the last section I mentioned “all the things functions are good for.” About this time, you might be wondering what exactly those things are. Here are some of the reasons functions are useful:

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By giving a name to a sequence of statements, you make your program easier to read and debug.
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Dividing a long program into functions allows you to separate parts of the program, debug them in isolation, and then compose them into a whole.
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Functions facilitate both recursion and iteration.
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Well-designed functions are often useful for many programs. Once you write and debug one, you can reuse it.
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For example, instead of writing the 53 lines of code below…

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#include <iostream>
using namespace std;

int main() {
    int x = 4;
    x = x * 2;
    x = x / 2;
    x = x + 2;
    x = x - 2;
    cout << x << endl;
    x = 13;
    x = x * 2;
    x = x / 2;
    x = x + 2;
    x = x - 2;
    cout << x << endl;
    x = 100;
    x = x * 2;
    x = x / 2;
    x = x + 2;
    x = x - 2;
    cout << x << endl;
    x = 22;
    x = x * 2;
    x = x / 2;
    x = x + 2;
    x = x - 2;
    cout << x << endl;
    x = 220;
    x = x * 2;
    x = x / 2;
    x = x + 2;
    x = x - 2;
    cout << x << endl;
    x = 0;
    x = x * 2;
    x = x / 2;
    x = x + 2;
    x = x - 2;
    cout << x << endl;
    x = 1000;
    x = x * 2;
    x = x / 2;
    x = x + 2;
    x = x - 2;
    cout << x << endl;
    x = 254;
    x = x * 2;
    x = x / 2;
    x = x + 2;
    x = x - 2;
    cout << x << endl;
}

..you would reduce it to the 21 lines of code below, making it easier to read, debug, and use the function many times with rewriting it each time.

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#include <iostream>
using namespace std;

void all_operators(int x) {
    x = x * 2;
    x = x / 2;
    x = x + 2;
    x = x - 2;
    cout << x << endl;
}

int main() {
    all_operators(4);
    all_operators(13);
    all_operators(100);
    all_operators(22);
    all_operators(220);
    all_operators(0);
    all_operators(1000);
    all_operators(254);
}

Checkpoint 6.7.1.

What is a function in C++?

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A named sequence/group of statements that perform a particular task.
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Yes, a function is a named sequence of statements.
Any sequence of statements.
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While functions contain sequences of statements, not all sequences of statements are considered functions.
A mathematical expression that calculates a value.
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While some functions do calculate values, the python idea of a function is slightly different from the mathematical idea of a function in that not all functions calculate values. Consider, for example, the turtle functions in this section. They made the turtle draw a specific shape, rather than calculating a value.
A statement of the form x = 5 + 4.
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This statement is called an assignment statement. It assigns the value on the right (9), to the name on the left (x).

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Checkpoint 6.7.2.

Create a function called absoluteValue, which returns the absolute value of a parameter num. Assume you do not have access to #include <cmath>.

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int absoluteValue(int num) {
---
void absoluteValue(int num) {  #distractor
---
int absoluteValue(int num)  #distractor
---
void absoluteValue(int num)  #distractor
---
  if (num > 0) {
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    return num;
  }
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  else {
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    int absNum = -(num);
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    return absNum;
  }
}

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Checkpoint 6.7.3.

What is of these is NOT a reason that functions are useful?

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Once you write and debug a function, you can reuse it.
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The reusability of functions is very useful.
Makes your program easier to read and debug.
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By abstracting blocks of code, functions make your code easier to read and understand.
Functions facilitate both recursion and iteration.
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Recursive functions and iterative functions are useful.
None of the above.
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All of the choices above are reasons for why functions are useful.

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