A **control flow path** (or control flow graph) is a graphical representation of the flow of a program.

Control flow paths represent all of the paths we can traverse during the execution of a program.

We use control flow paths most frequently for the *white box* testing of software.

# Properties 

A control flow graph is a directed graph. 

A control flow graph consists of two designated blocks:

1. Entry block
2. Exit block

As their names suggest, these blocks direct the entry and exit of the control flow into and out of the graph.

# Decision point

A decision point is a point in the control flow graph where the control of the program diverges. Common examples include `do-while` statements, `if` statements, and `case` statements.

These statements are also referred to as *control flow statements*.

# Example

We can better understand control flow paths by making one of our own.

Consider the following program:

#include <iostream>
using namespace std;


int main(){

	int a[100] = {0};
	
	for(int i = 0; i < 100; i++)
		a[i] = i;
		
	int temp;
	
	int x = 0;

	while (x < 100)
	{
	   if (a[x] % 2 == 0)
		  temp = 0;

	   else
		  temp = 1;

	   switch (temp)
	   {
		  case 0: cout << "a["<<x<<"] is even\n"; break;
		  case 1: cout << "a["<<x<<"] is odd\n"; break;
		  default: cout << "unexpected error\n";
	   }
	   x++;
	}

	return 0;
}


The above program declares and populates an array of size 100. Then, we check each array element to determine whether it is *even* or *odd*. 

Based on that, we set the value of `temp` (0 for even, 1 for odd).

For each element, the `switch` statement runs the `case` based on the value of `temp`.

Finally, the value for `x` is incremented after breaking out of the switch statement.

The control flow graph for the program is as follows:

The following is the breakdown of the control flow graph above:

1. The start of the `while` loop

2. The `if` statement

3. The branch we take if the `if` condition is true

4. The `else` statement

5. The `switch` statement

6. `case 0` statement

7. `case 1` statement

8. `default` statement

9. Increment (`x++`)

10. `return` statement

What is a control flow path?

A control flow path is a graphical representation illustrating all possible execution paths in a program, used primarily in white box testing.