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:

• By giving a name to a sequence of statements, you make your program easier to read and debug.

• 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.

• Functions facilitate both recursion and iteration.

• Well-designed functions are often useful for many programs. Once you write and debug one, you can reuse it.

For example, instead of writing the 53 lines of code below…

#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.

#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); }

Q-3: What is a function in C++?

• A named sequence/group of statements that perform a particular task.
• Yes, a function is a named sequence of statements.
• Any sequence of statements.
• While functions contain sequences of statements, not all sequences of statements are considered functions.
• A mathematical expression that calculates a value.
• 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.
• This statement is called an assignment statement. It assigns the value on the right (9), to the name on the left (x).

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

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

Q-5: What is of these is NOT a reason that functions are useful?

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

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