Goals of this course

• Introduction to the programming language C

• Learn how to program

• Learn ‘good’ programming practices

Programming

What is computer programming?

• Representation of a task or algorithm in a computer language.

What is an algorithm?

• A sequence of directions for accomplishing a task.

Example of an Algorithm

The algorithm for calculating the arithmetic mean(i.e., the average) of a set of numbers is1. add all the numbers together2. divide this sum by the number of numbers

In mathematical terms this is written as

Levels of Abstraction

Suppose a student is asked to come to the front of the class

• high-level – stand, walk to front

• mid-level – stand, turn 90◦ to the right, walk 15 feet, turn 90◦ to the left, walk 10 feet

• low-level – contract specific muscles in a specific order

• lowest-level – you think about walking, initiating many electrochemical reactions

Levels of Abstraction cont.

Computer languages that correspond to these levels of abstraction:

• high-level – perl, python, matlab

• mid-level – C

• low-level – assembly language

• lowest-level – machine code

Analyzing a Problem

Computers understand concrete steps, not abstract concepts.

To determine the concrete steps involved in solving a problem, we may

• Represent the problem using pseudocode

• Work through the process using a simpler or smaller version of the problem

Analyzing a Problem cont.

Example: You must sort 1000 numbers in ascending order.

Simpler version: Sort 3, 2, 4, 1 in ascending order

Pseudocode:

Basic Concepts

Much of programming consists of the following:

• Storing and updating information – Variables and Statements

Example: store the answer given by a user

• Making decisions – ConditionalsExample:if temperature > 150 degrees

print ‘‘It’s too hot!’’

• Repeating certain tasks – LoopsExample: calculate the first 1000 prime numbers

Basics of CExample Code

#include<stdio.h> #define PI 3.14159

/* Finds the area and circumference of circle with radius r */ main ( void ) { double radius, /* radius of circle */ circumference, /* circumference of circle */ area; /* area of circle */

/* get radius of circle */ printf( “Please enter radius: “ ); scanf( “%lf”, &radius );

/* compute area and circumference */ area = PI * radius * radius; circumference = 2 * PI * radius;

/* display the result */ printf(“The area of the circle is %f and its circumference is %f\n”,

area, circumference); } /* main */

Basics of CForm of a Simple C Program

Preprocessor directives

main ( void )

{

declarations

executable statements

}

Basics of CPreprocessor Directive

#include <standard header file>

The C language includes only a minimal set of operations

Many useful functions and symbols are contained in libraries

Each library has a standard header file which has a name ending in .h

The #include instruction gives a program access to the corresponding library

Example: #include <stdio.h>

• gives access to (among others) the library functions scanf and printf which allow reading input from the keyboard and writing to the monitor

Basics of CPreprocessor Directive

#define NAME constant_value

This tells the preprocessor to replace every instance of NAME with the constant_value.

Makes the program easier to read, write, and maintain.

Example:

#define PI 3.14159

#define NUM_STUDENTS 85

#define OZ_PER_POUND 16

Basics of CFunction main

Every C program has a main function

Program execution begins with main function

main ( void ) is the main function heading

{ } braces are used to enclose the body of the function

Basics of CDeclarations

Declarations tell the compiler to set aside space for variables

Types are associated with the variables

The declaration:

double radius;

– tells the compiler space is needed for a variable named radius, and that it will be used to store doubles (reals).

Basics of CDeclarations and Data Types

General Syntax of a variable declaration:

type variable_list;

examples:

int count;

double radius,

area,

circumference;

char initial, code;

int for integers

double for real numbers

char for individual characters

Basics of CReserved Words and Standard

Identifiers

Reserved words have special meaning in C and cannot be used for anything else in the program

Must be lower case

Examples: int, double, void, return

Standard identifiers also have a special meaning in C, but they can be redefined by the programmer (though it is not a good idea).

Examples: printf, scanf

Basics of CUser-Defined Identifiers

Users create their own identifiers to name the variables and other items in the program (e.g. to name functions other than main)

Rules for creating user-defined identifiers:may contain only letters, digits, underscorecannot begin with a digitcannot contain spacescannot be reserved wordshould not be a standard identifier

Correct: Incorrect:

sum sum#1

hours_worked hours worked

R2D2 2R2D

MyVal My-Val

goodint int

Basics of CExecutable Statements

Executable statements tell the computer to take action during the running of the program

Statements are terminated by a semicolon

Examples:

• Assignment

area = PI * radius * radius;

• Input function

scanf( “%lf”, &radius );

• Output function

printf(“The area of the circle is %f and its circumference is %f\n”,area, circumference);

Basics of CComments

Comments are used to document programs

Syntax: /* text of comment */

Listed in the program but ignored by the compiler

Can go across lines, until terminating */ is written

Programs should begin with comments (This is called the Header Section). They should contain at least:

your namedue datelab numberlab sectionlab instructors namebrief description of the program

Comments should be used throughout to document the declaration of variables and main algorithm steps