CS1101C Lab 1 (Even Week)

Multiplication

The deadline for this lab question is Wednesday 14 September 2005, 23:59:59 hours.

The name of your C program file must be called multiply.c, files with any other name will not be marked.

You are expected to spend a maximum of 2 hours for this assignment.

The Task

Nemo's kid wants to learn long multiplication. Gosh, it has been ages since you've did it! Now with calculators and computers, you merely press the numbers into the device and the answer pops out.

But kids must learn long multiplication the long way. Nemo has totally forgotten how to do it; so he asks you to write a program that shows long multiplication.

Here are two sample runs of the program that Nemo wants. Note that $ indicates the Unix prompt, and you are reminded to follow the sample runs exactly, else marks will be deducted. User input is underlined.

$ gcc -Wall multiply.c -o multiply
$ ./multiply

Enter two integers to multiply: 9876 5432

     9876
   x 5432
---------
 49380
  39504
   29628
+   19752
---------
 53646432
---------

$ ./multiply

Enter two integers to multiply: 2345 608

     2345
   x  608
---------
     0
  14070
       0
+   18760
---------
  1425760
---------

$

Let's look at the first example:

  1. 9876 is multiplied with 5 to give 49380. It is shifted three places to the left since it shows the value in thousands.
  2. 9876 is multiplied with 4 to give 39504. It is shifted two places to the left since it shows the value in hundreds.
  3. 9876 is multiplied with 3 to give 29628. It is shifted one place to the left since it shows the value in tens.
  4. 9876 is multiplied with 2 to give 19752. It is not shifted.
  5. The answer of 53646432 is obtained by adding up the above four intermediate values (after multiplying each intermediate value with an appropriate number if necessary). You are not allowed to obtain the final answer directly by calculating 9876 * 5432.
You may assume that the numbers entered by the user will be between 0 to 9999 inclusive.
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