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haas:spring2015:cprog:projects:afn0 [2015/02/25 14:39] – [Function prototype] wedge | haas:spring2015:cprog:projects:afn0 [2015/03/20 20:45] (current) – [Prerequisites/Corequisites] wedge | ||
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* can perform this trick in your head/by hand (if you can't do it on your own, you have no business trying to tell the computer how to do it) | * can perform this trick in your head/by hand (if you can't do it on your own, you have no business trying to tell the computer how to do it) | ||
- | * understand the pattern/ | + | * understand the pattern/ |
* ability to deploy loops to simplify your process | * ability to deploy loops to simplify your process | ||
* ability to use arrays to facilitate the storage of your processed values | * ability to use arrays to facilitate the storage of your processed values | ||
Line 167: | Line 167: | ||
} | } | ||
</ | </ | ||
- | ====Using loops and arrays together for universal harmony==== | ||
- | To really make the most out of arrays in scaling | + | ====function calling==== |
+ | Once we've declared (prototyped) and defined | ||
- | ===42 everywhere=== | + | Here would be an example of calling the above-mentioned |
- | + | ||
- | To illustrate, here we will declare | + | |
<code c> | <code c> | ||
- | int data[11], position | + | int scores[4]; |
+ | int tally = 0; | ||
- | for(position = 0; position < 11; position=position+1) // see, using long form, could have done " | + | scores[0] = 88; |
- | { | + | scores[1] = 47; |
- | data[position] = 42; | + | scores[2] = 96; |
- | } | + | scores[3] = 73; |
- | </ | + | |
- | ===Display array contents=== | + | tally = sum(scores, 4); |
- | What if we wanted to print the contents of the array? Once again, we use a loop, and print out each value, one at a time. | + | |
- | + | ||
- | Important considerations: | + | |
- | * again, with C, being true to how the computer actually works, we can only access the array one element at a time | + | |
- | * because we know array indices start at 0, we have a known starting point | + | |
- | * because we know how big our array is (11 elements, from previous example), we know how many elements to go for | + | |
- | * each element is located one after the other-- 0 is followed by 1 is followed by 2 etc. | + | |
- | + | ||
- | ... therefore, we have all the ingredients for a **for** loop: | + | |
- | + | ||
- | <code c> | + | |
- | for (position = 0; position < 11; position++) | + | |
- | { | + | |
- | fprintf(stdout, | + | |
- | } | + | |
- | fprintf(stdout, " | + | |
</ | </ | ||
- | This should result in the following program output: | + | Note, that it is rather important to match the type and order of parameters. Due to the nature of the array (especially the form of array declaration) used, certain pointer-related details are being hidden from us, giving somewhat of a false impression. Further discussion about pointers will begin to shed light on that. |
- | <cli> | ||
- | 42 42 42 42 42 42 42 42 42 42 42 | ||
- | </ | ||
- | |||
- | ===Backwards? | ||
- | What if we wanted to display the contents of our array in reverse (from position 10 to position 9, to 8, down to 0)? | ||
- | |||
- | We'd still want to use a loop, but look at how we structure it: | ||
- | |||
- | <code c> | ||
- | for (position = 10; position >= 0; position--) | ||
- | { | ||
- | fprintf(stdout, | ||
- | } | ||
- | fprintf(stdout, | ||
- | </ | ||
- | |||
- | Notice how the loop-terminating relational statements differ (comparing the two-- for forward and backward, does it make sense?), and also how we progress between individual elements (in one we are incrementing, | ||
- | |||
- | That should make sense before you try to proceed. | ||
- | |||
- | ===Thinking with arrays=== | ||
- | Using arrays in your algorithms represents a potential barrier you have to overcome. Up until this point, we've been getting used to labelling all our variables with unique, individual names. | ||
- | |||
- | Now, with arrays, we have one common name, distinguishable by its element offset. That has been known to cause some conceptual problems due to the mildly abstract nature it creates. It would certainly not hurt to draw some pictures and manually work through some examples, step-by-step... it may be confusing at first, but the more you play with it, ask questions, play, read, etc., the sooner things will start to click. | ||
- | |||
- | As some of you have started to realize with **mbe0**, the actual core work of the project wasn't actually that hard, once you saw through the illusion of complexity we had placed in front of it. By using arrays, we can make our solutions even easier (and code even simpler)... but, we will initially have to eliminate self-imposed mental obstacles making the problem appear significantly more difficult than it actually is. | ||
- | |||
- | |||
- | ====Multiplying a number (of varying digits) by 11==== | ||
- | In **mbe0**, we specifically looked at 3 usage cases for our mental math problem: 1-, 2-, and 3-digit number. I limited it to those because, lacking arrays and loops for that project, the code would have gotten impossibly long and complex, plus: I wanted you to focus on the basics of variable usage and if-statements. | ||
- | |||
- | Now that we have those down, we can now apply arrays and loops to optimize and enhance a solution, and to allow it to scale to a wider range of possibilities (why limit ourselves to just 1-, 2-, and 3-digit values? Once we see the pattern, we can apply this to 4-, 5-, 6-digit numbers and beyond). | ||
- | |||
- | ===3-digits (review)=== | ||
- | Again, to review, let's look at a 3-digit example. 123 x 11: | ||
- | |||
- | < | ||
- | 123 x 11 = 1 (1 + 2) (2 + 3) 3 | ||
- | = (1 + 0) (3 + 0) 5 | ||
- | = 1 | ||
- | = 1353 | ||
- | </ | ||
- | |||
- | And digit-based additions that generate a carry are similarly propagated. | ||
- | |||
- | 567 x 11: | ||
- | |||
- | < | ||
- | 567 x 11 = 5 (5 + 6) (6 + 7) 7 | ||
- | = (5)+1 | ||
- | = 6 | ||
- | = 6237 | ||
- | </ | ||
- | |||
- | When doing this, we need to evaluate the number from right to left (just as we would do it if we were to compute it purely mathematically by hand): | ||
- | |||
- | * We know the last digit (1s place) of 567 x 11 right off the bat: 7 | ||
- | * The second digit (10s place) is the sum of 6 and 7 (6+7) which is 13 (sum of 3, carry of 1), so: 3 | ||
- | * The third digit (100s place) is the sum of 5 and 6 plus any carry from the 10s place (which is 1), so (5+6+1) which is 12 (sum of 2, carry of 1), so: 2 | ||
- | * The fourth digit (1000s place) is the original first value (5 of the 567) plus any carry from the 100s place (which there is, a 1), so (5+1) which yields a sum of 6, carry of 0. | ||
- | |||
- | A dual benefit of this project is that in addition to extending your programming experience / understanding of C, you could develop this as a mental ability (that is where it originated), | ||
- | |||
- | ===4-digits=== | ||
- | Now let us process a 4-digit example (look for similarities to the 3-digit process, specifically how this is merely an expansion, or an additional step-- due to the additional digit): | ||
- | |||
- | 4567 x 11: | ||
- | |||
- | < | ||
- | 4567 x 11 = 4 (4 + 5) (5 + 6) (6 + 7) 7 | ||
- | = (4)+1 | ||
- | = 5 | ||
- | = 50237 | ||
- | </ | ||
- | |||
- | Remember, we are processing this from right to left (so that the carry values can properly propagate). While there is no initial carry coming in, we'll add one anyway (0), so we see 13+0 (which is simply 13)... but because we're interested in place values, this is actually a sum of 3, carry of 1... and that one gets sent over to the next place (which has an 11)... so 11+1 will be 12, or sum of 2, carry 1... that carry will propagate to the next position to the left (the 9)... so there' | ||
- | |||
- | Can you see how "the same" this process for 4-digit numbers is when comparing to the process for 3-digit numbers? And how the same comparison can be made for 2-digit, and 5-digit, 6-digit, etc.? Please take some time, working through some examples (by hand) to identify and notice the pattern, or essence, of this process. You need to see how it doesn' | ||
- | |||
- | That " | ||
- | (Also, the potential exception here would possibly be 1-digit values... if you cannot easily find a way to make 1-digit numbers work with greater-than-1-digit numbers, that's where an if-statement would come into play-- if 1-digit, do this specific process, else do the regular process). I'm not saying one universal solution isn't possible, but at this stage of your structured programming development, | ||
=====Program===== | =====Program===== | ||
- | It is your task to write an optimized version of your multiply by eleven | + | It is your task to write a program that obtains a long integer value from the user, and processes that single value into separate array elements |
Your program should: | Your program should: | ||
* obtain its input from STDIN. | * obtain its input from STDIN. | ||
- | * input should be in the form of a single integer value | + | * input should be in the form of a single |
* determine the number of digits of the inputted value (store this in a variable) | * determine the number of digits of the inputted value (store this in a variable) | ||
- | * perform the correct algorithm against | + | |
- | * propagate any carries | + | * you may assume a maximum array size of the maximum number of digits you're theoretically able to input that can be stored in a 64-bit value. |
- | * use an array (**digit**) to store individual digits from the number input | + | |
- | * use another | + | * display the problem being solved, along with the answer |
- | * hint: you will want to make the **result** array one element larger. Why is this? | + | * use functions to modularize your code: |
- | * Display output showing aspects of the process | + | * have an **longint2array()** function that takes the long int, and returns an array (the function itself handles the processing |
- | | + | * have a **printarray()** function, whose responsibility it is to display the indicated |
+ | * have a **allfromnine()** function that takes the source array, does the processing, and returns ther result | ||
- | =====Execution===== | + | I might suggest the following function prototypes: |
- | Several operating behaviors are shown as examples. | + | |
- | An eight digit value: | + | <code c> |
+ | unsigned char *longint2array(unsigned long int); | ||
+ | void printarray(unsigned char *, unsigned char); | ||
+ | unsigned char *allfromnine(unsigned char *); | ||
+ | </ | ||
- | < | + | Some questions to contemplate: |
- | lab46:~/ | + | |
- | Enter value: 31415926 | + | |
- | Digits detected: 8 | + | |
- | Obtaining unique digits, storing in array... | + | * Why an array of unsigned chars when we're starting with a long (long) int? |
- | digit[0] = 6 | + | * Why is that the "best fit" size-wise? |
- | digit[1] = 2 | + | * Why will that not result in lost data? |
- | digit[2] = 9 | + | * Why unsigned? |
- | digit[3] = 5 | + | * What impact will that have on our input value' |
- | digit[4] = 1 | + | * Why represent the size of the usable array as an unsigned char? |
- | digit[5] = 4 | + | * Why is this the "best fit" size-wise? |
- | digit[6] | + | =====Execution===== |
- | digit[7] | + | An example |
- | + | ||
- | Applying process... | + | |
- | result[0] | + | |
- | result[1] | + | |
- | result[2] | + | |
- | result[3] | + | |
- | result[4] | + | |
- | result[5] | + | |
- | result[6] | + | |
- | result[7] | + | |
- | result[8] = 3 + 0 + 0 (sum of 3, carry out of 0) | + | |
- | + | ||
- | Displaying result... | + | |
- | 31415926 x 11 = 345575186 | + | |
- | lab46: | + | |
- | </ | + | |
- | + | ||
- | Next, a four digit value: | + | |
<cli> | <cli> | ||
- | lab46: | + | lab46: |
- | Enter value: | + | Enter value: |
- | Digits detected: | + | Digits detected: |
- | Obtaining unique digits, storing in array... | + | |
- | digit[0] = 4 | + | - 31415926535897 |
- | digit[1] = 0 | + | --------------- |
- | digit[2] = 1 | + | |
- | digit[3] = 7 | + | |
- | Applying process... | + | lab46: |
- | result[0] = 4 + 0 + 0 (sum of 4, carry out of 0) | + | |
- | result[1] = 0 + 4 + 0 (sum of 4, carry out of 0) | + | |
- | result[2] = 1 + 0 + 0 (sum of 1, carry out of 0) | + | |
- | result[3] = 7 + 1 + 0 (sum of 8, carry out of 0) | + | |
- | result[4] = 7 + 0 + 0 (sum of 7, carry out of 0) | + | |
- | + | ||
- | Displaying result... | + | |
- | 7104 x 11 = 78144 | + | |
- | lab46: | + | |
</ | </ | ||
- | |||
- | Finally, a five digit value: | ||
- | |||
- | <cli> | ||
- | lab46: | ||
- | Enter value: 56789 | ||
- | Digits detected: 5 | ||
- | |||
- | Obtaining unique digits, storing in array... | ||
- | digit[0] = 9 | ||
- | digit[1] = 8 | ||
- | digit[2] = 7 | ||
- | digit[3] = 6 | ||
- | digit[4] = 5 | ||
- | |||
- | Applying process... | ||
- | result[0] = 9 + 0 + 0 (sum of 9, carry out of 0) | ||
- | result[1] = 8 + 9 + 0 (sum of 7, carry out of 1) | ||
- | result[2] = 7 + 8 + 1 (sum of 6, carry out of 1) | ||
- | result[3] = 6 + 7 + 1 (sum of 4, carry out of 1) | ||
- | result[4] = 5 + 6 + 1 (sum of 2, carry out of 1) | ||
- | result[5] = 5 + 1 + 0 (sum of 6, carry out of 0) | ||
- | |||
- | Displaying result... | ||
- | 56789 x 11 = 624679 | ||
- | lab46: | ||
- | </ | ||
- | |||
- | The execution of the program is short and simple- obtain the input, do the processing, produce the output, and then terminate. | ||
=====Submission===== | =====Submission===== | ||
Line 409: | Line 253: | ||
<cli> | <cli> | ||
- | $ submit cprog mbe1 mbe1.c | + | $ submit cprog afn0 afn0.c |
- | Submitting cprog project "mbe1": | + | Submitting cprog project "afn0": |
- | -> mbe1.c(OK) | + | -> afn0.c(OK) |
SUCCESSFULLY SUBMITTED | SUCCESSFULLY SUBMITTED |