Program line |
Description |
Algorithm block |

1 | In the 1st line of the program, we inform the browser that our document was written in HTML (more precisely, it is a header specific to HTML 5). Line 2 contains the <html> tag that begins the HTML code. The 3rd line starts the <body> section of our document, containing the elements that are to appear on the page. In our example, the <body> section contains only a script written in JavaScript that implements the algorithm for solving a quadratic equation. The <script> tag on line 4 informs about the start of the script. | - |

6 - 16 | We define the function linear that implements an algorithm for solving a linear equation. | 4 |

18-20 | We declare the variables a,b,c using the var keyword. At the same time, the assignment operator ("=") initializes these variables with user-entered values using the prompt() statement. prompt - JavaScript standard function - displays a text input pop-up on the screen. The first argument of the function specifies the text displayed as a prompt, the second is the default value entered in the edit field. As a result, the prompt() function returns the text entered by the user into the edit field and then confirmed with the OK button. |
2 |

21 | We check if the coefficient a is equal to 0. If so, we are dealing with a linear equation. | 3 |

22 | We will be in this line only when a = 0, i.e. when the equation is a linear equation. We call the function linear(b, c), which performs the algorithm for solving a linear equation. It is worth noting that the coefficient to the first power of x is denoted by b, and the intercept is c (traditionally, a and b are used respectively in a linear equation). | 4 |

23 | else, i.e. in the opposite case. At this point, the solution of the equation begins when a ≠ 0, i.e. when we are actually dealing with a quadratic equation. |
- |

24 | We declare a delta variable and calculate its value. | 5 |

25 | We check if delta < 0. | 6 |

26 | When delta < 0, we use the alert() function to print an appropriate message informing about the lack of solutions. |
7 |

27 | This is where the program block starts when delta is not lower than zero, i.e. when the equation has solutions (one or two). | - |

28 | We check if delta = 0. | 8 |

29 | We calculate and save in the variable x the solution of the equation (one double - delta = 0). | 9 |

30 | We display the calculated result. | 10 |

32 | We start the program block executed when the delta = 0 condition was not met (and the earlier delta < 0 and a ≠ 0). | - |

33 - 34 | We calculate the solutions and assign their values to x1 and x2 variables, which are also declared using the var instruction. |
11 |

35 | We display the calculated result - two solutions of the quadratic equation. | 12 |

46-37 | We close blocks of compound statements. | - |

39-41 | We close the tags </script>, </body> i </html>. | - |