Harvard Mark I Howard Aiken was a pioneer in computing and a creator of conceptual design for IBM in the 1940s. He envisioned an electro-mechanical computing device that could do a lot of monotonous and boring work instead of him. This computer was originally called the Automatic Sequence Controlled Calculator (ASCC). It was later renamed Harvard Mark I. The Harvard Mark I was completed in 1944, with help of Grace Hopper and IBM’s funding. The computer was 55ft long and 8ft tall. It weighed 5 tons and was made of about parts.

Bugs On September 9, 1947, Grace Hopper discovered the first computer bug. She was working as an operator on the Harvard Mark II computer when the operators were attempting to trace a problem in the hardware. Wedged into Relay #70 on Panel F was a large moth's body causing a short circuit. Hopper recorded and taped the find in the logbook as "The first actual case of bug being found".

Bugs Bugs have been an engineering term for many years. Thomas Edison was quoted in 1878 using the term bugs to refer to problems arising in the engineering process.

ERROR CORRECTION TECHNIQUES “Program Code has bugs not errors. Debugging is the process of finding and fixing errors.” Carole Wilson (SDD Prelim Course) p130

Types of Coding Errors Syntax Errors Occur when the code does not match the rules of the language. - Examples include - typos such as wmile instead of while or using the wrong type of brackets or other symbols - Forgetting punctuation such as a ; or. - Leaving out part of a statement such as not including an ENDIF after an IF - These errors usually show up when a program is compiled before execution, and are sometimes called Compile Errors

Types of Coding Errors Run Time Errors Show up while the program is running Can be a result of logic errors, overflow errors or undefined arithmetic operations Some common run-time errors that will not show up during program compile include: Mathmatical operations with non numeric data Dividing by zero Overflow errors usually occur when a calculation is performed on an incorrect data type and becomes impossible to store in the targeted memory location. Examples include: Assigning variables to the wrong type real number as an integer Array range errors where there are more variables in an array than have been declared

Types of Errors Logic Errors Often occur when implementing conditions or repetition Can occur when assigning values to variables Can be helpful to refer to your pseudocode and compare it to your actual code Include flags and step through your program while comparing expected and actual conditions and values

Debugging Tools Stubs Used to check connection between modules of code without the module of code existing Let you test the main logic or flow of the program Breakpoints Lets the developer indicate where in a program they want it to stop during execution Often the development environment will let you examine the value of variables as they were prior to hitting the breakpoint Flags A developer can introduce a flag to show a certain part of the code has been reached. A flag is a boolean variable that the developer can tested within the code Debugging Output Statements A developer can make a program print messages to the screen while a program is running to show that a particular point in the program was reached. A developer can also populate the display to show the value of a variable during program execution Visual Basic offers tools that allow the developer to follow the contents of a variable during execution