Creating a Project in XCode

Transcription

1 ECS 102 Lab 2 for Mac Spring 2018 Name Creating a Project in XCode 1. Creating a project and program file, and running a program. (a) If you have already installed XCode skip to Part b. Go to the App store and download XCode. Install for C/C++ development. (Talk to me first if you are not running Sierra or High Sierra.) (b) Following the instructions on the link < ecs102/lecture_labs/xcodehowto.html> i. Create a project folder ecs102. ii. Create a project labs. (c) Now you have the window you will be using for writing your programs. (d) Follow instructions at the same link to Add a new file (hello.c) (e) You should now see an empty white space, your edit window. Enter the following program. You ll notice that the editor takes care of most of the indentation, and even some of the symbols. /*hello.c My first ECS102 program*/ #include <stdio.h> int main() { printf ("Welcome to ECS 102. Hope you enjoy it here!\n"); return 0; } Save your program by clicking File Save or CTRL + S. (f) Return to XCode. To execute the program click Product Run or press Command + R. 1

2 If all went well, you should see a window on the bottom right with your program output in it. Read it. Once you recover from the awe of creating your first C program, you can continue. If all didn t go well and you had some errors: A red octagon appears next to lines of code with errors. Click on a marked line and an error message appears. Fix your first error and try to execute the program again. 2. Copying a program from the website. (a) Return to XCode. In the left panel select hello.c. Control click and choose Delete. A message box will come up. Press the Remove reference button, NOT the Move to Trash button. This will remove the file from the project, but leave it in the folder on the hard drive, so you can use it again later. (b) As before, you will create a file, this time called MilesToKM.c. (You will NOT need to create a new project!) Select the labs folder in the left panel. File New File MacOS, C file, Next give it the name MilesToKM.c and unclick Also create header file. labs, labs, labs click Create (c) In the edit window for MilesToKM.c, instead of typing code, open a web browser, go to the class website and navigate to Lectures and Labs, then in class 2 open the MilesToKM.c example by clicking on the link Miles to Kilometers code, select all and copy and paste the program into the file you just created. If the program is all in one line, do the following: (You will have to do this each time to enter a program into XCode.) Copy the program (again) from the website. Open TextEdit. Go to Format. If it says Make Rich Text choose that. If it says Make Plain Text do NOT choose that, you are already in Rich Text. Paste the code. Command+a to select all the code from TextEdit, then Command+c to copy. Paste into Xcode. Let me know if it still appears on one line. Run the program, Command+R Test the program. Give it some values where you know what the answer should be. For example you know that 1.0 mile should give you about 1.6 kilometers, so run the program entering 1.0 as input. Maybe you know that a kilometer is about 2

3 .6 miles, so run the program and enter.6 to see if you get about 1 kilometer. Then try some other values. In the table below, give the input value you tried, and fill in the output produced. (d) We rarely enter a program correctly, so it is a good idea to learn how to recognize and deal with errors. i. Remove double kms from double kms; /* output - distance in kilometers */ Run the program. A red octagon appears next to lines of code with errors. Click on a marked line and an error message appears. The error here is something like kms: undeclared identifier. Fix the line by putting double kms back and see that it runs properly. ii. One at a time create other errors. (Fix each error before you make the next one.) delete the & in the scanf statement, change the %f in the printf statement to %d, leave out one of the semicolons at the end of a line. See the computer s reaction. Does it complain? (Record the complaint - only the first error message.) Does it give an odd answer? (Record this.) Does it work fine? error 1(What error did you make?): computer s response (What error message did you get? get odd output?): Did you error 2: computer s response: error 3: computer s response: (e) Exploring data types 3

4 i. As you did earlier, remove the file MilesToKM.c and create a new file (not a project! use Project add new item) ExploreDataTypes.c Enter the code by copying from the website. ii. Run the program, and look at the output window. Enter values when asked. Make sure you first click in the output window. If you have errors, fix them. iii. Now you will run the program again while peeking into the memory. Move the cursor onto the line realnum=3.14; /* This is an assignment. (The first executable line) Debug Breakpoint Add breakpoint at current line. Run (Commant+R). Program will run to the line with the breakpoint. The line with the breakpoint will be highlighted. In the lower left window you will see the variables and their values. (Some look like 0, but are really just junk.) Check out the value or realnum. The highlighted line has not yet been executed. Click Debug StepOver. The next line, letter= M is highlighted. Check out the value of realnum - it has changed! But this line has not yet been executed so letter has a funky value. Click Debug StepOver again. The arrow has moved to the next line, printf("a whole number goes here: %d", wholenuma); and the previous line has been executed. Look in the Locals window and check out the value of letter. Keep clicking Debug StepOver, each time watching the variables in the Locals window as described below: At each line, read the code, try to figure out what it will do, then check if you were right. If not, go back and look at the code to understand EXACTLY how it works. * When you come to a printf statement, after executing the line, look at the output window to see what appears. * If you click on the output window to see it better, you will need to click on the title bar of the program window before you can continue stepping through the program. * When you come to the scanf statements: with the scanf statement (not yet executed) highlighted, click Debug StepOver. The highlight disappears, and the output window becomes active, with a cursor blinking. 4

5 Enter a number and press the enter key. Control should go back to the program window. * (If the program window is not the active window you may need to click on the title bar of the program window to make it active again. ) The highlight should have moved on to the next line. See where the value you entered appears in the Locals window. Step through the whole program this way. When the linereturn 0; is highlighted stop debugging. (f) Printing the output (what appears in the output window): Click in the output window. Command+a to select all, Command+c to copy Paste it into a text window, either using XCode or some other text editor, like TextEdit. You can print the program within XCode in the File menu. Make sure your cursor is in the program pane so the program file window is selected. I ll let you know what printer we should use. Put your name and section on the output and the program. Put your name and section on the top of the first page of the lab packet, and turn in this lab packet, the program, and the output. 5