Section 1.4 - IT 140_ Introduction to Scripting _ zyBooks

 Students: Section 1.4 is a part of 1 assignment: 1-3 zyBooks Participation Activities Includes: PA 1.4 Errors Syntax errors As soon as a person begins trying to program, that person will make mistakes. One kind of mistake, known as a syntax error , is to violate a programming language's rules on how symbols can be combined to create a program. An example is putting multiple prints on the same line. The interpreter will generate a message when encountering a syntax error. The error message will report the number of the offending line, in this case 7, allowing the programmer to go back and ±x the problem. Sometimes error messages can be confusing, or not particularly helpful. Below, the message "invalid syntax" is not very precise, but is the best information that the interpreter is able to report. With enough practice a programmer becomes familiar with common errors and is able to avoid them, avoiding headaches later. Note that syntax errors are found before the program is ever run by the interpreter. In the example below, none of the prints prior to the error is in the output. Figure 1.4.1: A program with a syntax error. print ( 'Current salary is' , end = ' ' ) print ( 45000 ) print ( 'Enter new salary:' , end = ' ' ) new_sal = int ( input ()) print ( new_sal ) print ( user_num ) File "<main.py>", line 7 print(new_sal) print(user_num) ^ SyntaxError: invalid syntax PARTICIPATION ACTIVITY 1.4.1: Syntax errors. Find the syntax errors. Assume variable num_dogs exists. 1) print(num_dogs). Error No Error 2) print("Dogs: " num_dogs) Error No Error 3) print('Woof!") Error No Error 4) print(Woof!) Error No Error 5) print("Hello + friend!") Error No Error PARTICIPATION ACTIVITY 1.4.2: Common syntax errors. Find and click on the 3 syntax errors. Feedback? Feedback?

1) triangle_base = 0 # Triangle base (cm) triangle_height = 0 # Triangle height (cm) # Triangle area (cm) print('Enter triangle base (cm): ') print('Enter triangle height (cm): ') triangle_area = (triangle_base * triangle_height) / 2 print(triangle_base) print(') / 2 = ', end=' ') print(triangle_area, end=' ') Good coding practice New programmers will commonly write programs with many syntax errors, leading to many frustrating error messages. To avoid continually encountering error messages, a good practice is to execute the code frequently, writing perhaps a few (3–5) lines of code and then ±xing errors, then writing a few more lines and running again and ±xing errors, and so on. Experienced programmers may write more lines of code each time, but typically still run and test syntax frequently. PARTICIPATION ACTIVITY 1.4.3: Run code frequently to avoid many errors. PARTICIPATION ACTIVITY 1.4.4: Testing for syntax errors. 1) Experienced programmers write an entire program before running and testing the code. True False Runtime errors The Python interpreter is able to detect syntax errors when the program is initially loaded, prior to actually executing any of the statements in the code. However, just because the program loads and executes does not mean that the program is correct. The program may have another kind of error called a runtime error , wherein a program's syntax is correct but the program attempts an impossible operation, such as dividing by zero or multiplying strings together (like 'Hello' * 'ABC'). A runtime error halts the execution of the program. Abrupt and unintended termination of a program is often called a crash of the program. Consider the below program that begins executing, prints the salary, and then waits for the user to enter an integer value. The int() statement expects a number to be entered, but gets the text 'Henry' instead. Figure 1.4.2: Runtime errors can crash the program. The program crashes because the user enters 'Henry' instead of an integer value. print ( 'Salary is' , end = ' ' ) print ( 20 * 40 * 50 ) print ( 'Enter integer: ' , end = ' ' ) user_num = int ( input ()) print ( user_num ) Salary is 40000 Enter integer: Henry Traceback (most recent call last): File "<stdin>", line 5, in <module> ValueError: invalid literal for int() with base 10: 'Henry' triangle_area = 0 triangle_base = int(input() triangle_height = int(input()) # Calculate triangle area Print out the triangle base, height, and area print('Triangle area = (', end=' ') print(*, end=' ') print(triangle_height, end=' ') print('cm**2') Feedback? Run code Run code Run code Run code stmt1 stmt2 stmt3 stmt4 stmt5 stmt6 stmt7 stmt1 stmt2 stmt3 stmt4 stmt5 stmt6 stmt7 1. Writing many lines of code without compiling is bad practice. 2. New programmers should compile their program after every couple of lines. Captions  Feedback? Feedback? Start 2x speed

Activity summary for assignment: 1-3 zyBooks Participation Activities 98 % 98 % submitted to desire2learn Figure 1.4.4: The ±rst bug. A sidenote: The term "bug" to describe a runtime error was popularized in 1947. That year, engineers working with pioneering computer scientist Grace Hopper discovered their program on a Harvard University Mark II computer was not working because a moth was stuck in one of the relays (a type of mechanical switch). They taped the bug into their engineering log book, which is still preserved today ( http://en.wikipedia.org/wiki/Computer_bug ). CHALLENGE ACTIVITY 1.4.1: Basic syntax errors. Retype the statements, correcting the syntax error in each print statement. print('Predictions are hard.") print(Especially about the future.) user_num = 5 print('user_num is:' user_num) Learn how our autograder works 553398.3976864.qx3zqy7 How was this section? | Load default template... num_beans = 500 num_jars = 3 total_beans = 0 print ( num_beans , 'beans in' , end = ' ' ) print ( num_jars , 'jars yields' , end = ' ' ) total_beans = num_beans * num_jars print ( 'total_beans' , 'total' ) Run Feedback? Feedback? ''' Your solution goes here ''' Run View your last submission  Feedback? Provide section feedback Completion details  1 2 3 4 5 6 7 8 9 1 2 3