EPSII

59:006

Spring 2004

Introduction to C

More Administrative Details The C Programming Language How a computer processes programs Your first C program Anatomy of a C program

More Administrative Details

Evening Exams Will try to have T.A.’s in lab by Monday

(1245 SC) Accessing Unix systems

Course web page

http://www.engineering.uiowa.edu/~eng006

Note: use webCT4.1

Exams: concurrent exams at nightUnified HW assignmentsGrading uniform across all sections.

Introduction to the C Programming Language C is a powerful high-level programming

language that also maintains the ability to do some low-level stuff

With the power of C comes both freedom and responsibilityThe language’s rules allow for many different

programming techniquesThis freedom can get you into trouble!

Writing C Programs

In this course you will learn one consistent approach to writing C programs (and pick up much information common to any way of writing these programs)

If you try hard to conform to the guidelines presented, you will be up and running with a minimum of difficulty

How does a computer process a user program?

A simple C program

Compiling, linking, and running

Next, compile, link, and run your program:% gcc simple.c –o simple

% simple

I am a simple computer.My favorite number is 1 because it is first.

%

Anatomy of a C Program

Anatomy of a C Program

Fundamental Aspect of a C Program: Everything is a function! Functions are blocks, and curly braces { and } delimit blocks So,

int main(void){ …….

.…… return 0;

}

Is a function Well learn more about functions in a moment

Anatomy of a C Program The main () function

Tells the compiler to start with this function Calls other functions in your program Example:

int f1(void){ return 1;}

int f2(void) {

return1;}

int main(void){ f1(); f2(); return 0;}

Anatomy of a C Program

#include<stdio.h>

This is actually a pre-processor statement that includes a header file (note the .h extension) which describes the standard I/O library functions (needed for printf() in this program).

Anytime you use functions from external libraries you should include a header file to tell the compiler about the function you are using.

Anatomy of a C Program

Variables are symbolic names referring to storage in computer memory

All variables must be declared in Cvariable declaration:

int num; All variables must be defined before use:

variable definition:num = 1;

Anatomy of a C Program

Variables Must refer to a specific amount of computer storage

(in bytes), but you don’t have to worry about the details – for now you can just use a pre-defined type.

Some Predefined Variable Types int – integer (positive or negative whole number) char – character variable (holds a code describing a character) double – double-precision floating point, a real number float – single-precision floating point number

Anatomy of a C Program

Where to Declare Variables In C, you must declare all variables first in a

function (this includes main()) Where to Define Variables

Although you can define (initialize) variables anywhere in a function, you usually do it at the top for readability

Anatomy of a C Program

Each of these lines of code are called statements

Statements always are terminated with a semicolon ‘;’

Functions can return a value:int f1(void);

Or, functions can return nothing:void f1(void);

Anatomy of a C Program

Functions also take 0 or more arguments, separated by commas:Examples:

int main (void); /* no arguments */int f1(int); /* a single integer argument */

int f2(int, int); /* two integer arguments */

Example program: Adding two numbers

Let’s say you want to add two numbers:

int main(void){ int num1,num2,sum;

num1 = 1; num2 = 2; sum = num1 + num2; printf("The sum of %d and %d is %d\n", num1,

num2, sum); return 0;}

Writing to the screen

Use the printf() function:”

#include <stdio.h>

printf(”This goes to the screen without a new line”);

printf(”This gets a new line\n”);

Writing to the screen

Escape Sequences

\n new line

\a alert (rings terminal bell)

\t tab

\\ Prints a backslash

\*

*/

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