Writing a computer program is like creating a recipe

Sridhar NarayanDepartment of Computer Science

narayans@uncw.edu

Program vs. a recipe - 1A recipe describes a culinary process that

produces a dishDifferent recipes produce different dishesThe same dish may have different recipes

(variations on a theme)A computer program describes a

computation process that produces one or more resultsDifferent programs describe different computationsThe same computation can be described by

different programs

Program vs. a recipe - 2A recipe is a script

Script is written by the author of the recipeAuthor envisions the dish to be produced and

creates the corresponding recipeA computer program is a script

Script written by the programmerProgrammer envisions the computational

process to be performed and creates the appropriate program

Program vs. a recipe - 3A chef follows a recipe

Chef may have some freedom to deviate from the script and improvise

In a computer program, the computer (i.e. CPU) follows the programCPU has no freedom to deviate from the

script. It follows it exactly as written.

Program vs. a recipe - 4The recipe must be written in a language the

chef understandsIf the author of the recipe writes in a foreign

language, the recipe must be translated before the chef can use it

A computer’s native language is machine languageIf the computer program is written in a foreign

language, i.e. non machine-language, it must be translated before it can be executed. A compiler is a computer program that performs this translation.

Program TranslationYou can write computer programs in any

language for which such a translator exists, or can be written

At this time, translators do not exist (nor is it known how to write them) for natural languages, i.e. English, Spanish, German, Russian etc.

Programming LanguagesA computer programming language is

typically English-like but is considerably more restrictive

Like natural languages, a computer programming language has a vocabulary and rules of grammar.

You have to be familiar with the vocabulary and the rules of a programming language before you can write computer programs in it.

The C programming languageJava, Python, Fortran, C, are all examples of

programming languages.In this class, you will be programming in a

language named C.

Program vs. a recipe - 5The recipe author may use a text editor (like

Notepad) or a word processor to write the recipe.Note that the word processor cannot write the

recipe on its own. However, it may help the process, for example by providing templates for recipes.

A programmer may use a text editor (like Notepad) to write the computer programNote that the editor cannot write the program

on its own. However, it may help the process, for example by providing templates for programs.

Program vs. a recipe - 6An Interactive Development Environment

(IDE) like Code::Blocks is an environment that allows a programmer to use a single interface to conveniently:Write the program using an editorCompile itDebug itExecute itRevise it

Program vs. a recipe - 7An involved recipe may be divided into many

parts. For example, preparation the night before, preparation right before you cook, etc.

A C program may be divided into many functions, each of which has a unique name.Execution of a C program always begins

with a function named main.Initially, all the programs you write will feature

only the main function. Later, you will write programs that define other functions besides main.

Program vs. a recipe - 8Recipe

Has many stepsChef follows the steps in sequence, starting with step 1Later steps often depend on the results of earlier steps

A C programHas many statementsComputer follows the statements in sequence, starting

with statement 1Statements that appear later in a program often

depend on the results of statements that appear earlier

Recipe exampleList of ingredients

3 potatoes1 cup olive oil1 teaspoon salt

Detailed description of what to do, in what order, with those ingredients1. Chop potatoes into 1 inch cubes2. Grease baking sheet with olive oil3. Spread potatoes evenly on baking sheet4. Roast potatoes at 300 degrees Fahrenheit for 10

minutes5. Season with the salt.

Computer program: ingredientsList of variables. Think of these as

ingredients for a computation.Each variable has a name: x, y, gradeEach variable has a type : int, float, doubleA type specifies what values can be assigned to

that variable. For example, int – integers, i.e. whole numbers without a

fractional component. For example, 10, 34, 23456. float – floating point numbers, i.e. numbers that

can have a fractional component. For example, 12.2, 345.102

Example: int a = 24;

Computer programA detailed description of what operations

need to be performed, in order, using the variables

A simple C program#include <stdio.h>#include <stdlib.h>

int main(void) {

int a, b, c;

a = 10;

b = 20;

c = a + b;

printf(“Here is the result\n”);

printf(“%i + %i = %i\n”, a, b, c);

return 0; //that says return zero

}