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Let us look at procedure abstraction using a children's nursery rhyme as an example.

Note: Using a simple song has the advantage that the output is known and easily recognizable while one is programming the abstractions.

Here are the lyrics to the song, "Mary had a little lamb".

Obviously, we could output this text using print statements as follows.
printf("Mary had a little lamb,\n"); printf("little lamb, little lamb\n"); printf("Mary had a little lamb,\n"); printf("it's fleece was white as snow.\n"); printf("\n"); printf("And everywhere that Mary went,\n"); printf("Mary went, Mary went.\n"); printf("Everywhere that Mary went,\n"); printf("the lamb was sure to go.\n");

Here is a program to do just that.

Here is the C code.
#include <stdio.h> int main() { printf("Mary had a little lamb,\n"); printf("little lamb, little lamb\n"); printf("Mary had a little lamb,\n"); printf("it's fleece was white as snow.\n"); printf("\n"); printf("And everywhere that Mary went,\n"); printf("Mary went, Mary went.\n"); printf("Everywhere that Mary went,\n"); printf("the lamb was sure to go.\n"); return 0; }
The output is as expected.

Here is the output of the C code.
Mary had a little lamb, little lamb, little lamb Mary had a little lamb, it's fleece was white as snow. And everywhere that Mary went, Mary went, Mary went. Everywhere that Mary went, the lamb was sure to go.

But suppose we also want the following output.

And then the following requirement.

And there may be more in the future.

Do you see that there are similarities and differences. Some abstractions are in order.

A common example of such requirements are a web page system that must generate certain output or reports based on data in a database.

A mail-merge process using, say, a template in Microsoft Word and a database of differences in an Excel worksheet is another example.

In the mail merge process, the differences (fields from each database record) are merged into the similarities (document with fill-in fields) to create the collection of documents merged documents

From the above text, one should be able to visually see and identify the differences. Here is a table of the above differences.

Names for differences
Name	v. 1	v. 2	v. 3
NAME	Mary	Johnny	Susan
SIZE	little	tiny	hopping
ANIMAL	lamb	pig	rabbit
FUR	fleece	hide	fur
COLOR	white	black	brown
OBJECT	snow	coal	earth

Note that the generic name given the difference need not match all instances. It is sufficient that it has some general meaning for the programming process.

Suppose one does not see the differences. Here is a color-coded table of differences.

Names for differences
Name	v. 1	v. 2	v. 3
NAME	Mary	Johnny	Susan
SIZE	little	tiny	hopping
ANIMAL	lamb	pig	rabbit
FUR	fleece	hide	fur
COLOR	white	black	brown
OBJECT	snow	coal	earth

And here are the above versions of the text, color-coded.

Here, again, is the color-coded table of differences.

Names for differences
Name	v. 1	v. 2	v. 3
NAME	Mary	Johnny	Susan
SIZE	little	tiny	hopping
ANIMAL	lamb	pig	rabbit
FUR	fleece	hide	fur
COLOR	white	black	brown
OBJECT	snow	coal	earth

We can now created input data sets for each of the above (and other, if necessary) versions.

Above is the logical input. To become physical input, some decisions need to be made.

• Are there other data in the input, such as a debug output setting.
• How is the above data recognized: counter loop, header loop, trailer loop (what is the trailer value), endfile loop, or some other way.

Some ways of creating a program to take the input data and output the text to each of the songs using that data will now be covered. The following approaches will be used.

• Individual variable solution: C: Procedural abstraction using variables
• Array solution: TBA
• Record structure solution: TBA