introduction to “programming in c” lone leth thomsen

Introduction to “Programming in C”

Lone Leth Thomsen

February 2006 Basis-C-1/LL 2

Contents

• Introduction to the course– Purpose, literature

• Mini project/evaluation

• Today’s topics (easy start)


Introduction to the course

• Purpose– “a give jer en grundlæggende

programmeringsfærdighed OG en forståelse af datalogiske grundbegreber knyttet til data, kontrol, algoritmer, abstraktion, struktur og korrekthed”

• Notice ”og-delen”, here the focus is on understanding and not just the ability to write programs


Practical info

• Lectures Thursday 8.15 - 10.00

• Exercises Thursday 10.15 - 12.00

• 10 modules, SE course– 8 lectures with exercises– 2 modules used on larger exam exercise


Mini project/evaluation

• Larger programming exercise as starting point• 2 modules ”reserved” for this• Solved in half-groups• The solution has to be design considerations as

well as an executable program• CD, description and print-out• Questions to program as well as course curriculum• Examination in half-groups, individual evaluation


Why do we write programs?

• To implement algorithms that are designed to solve problems

• Programs are important in system design

• Lots of examples and applications, some concrete, others more abstract


Analysis

• Analysis of a problem involves identification of input and output as well as requirements and limitations

• This requires that you can specify the problem in a clear and unambiguous way


Algorithm design

• Try not to solve all the problem details from the beginning – you’ll never get any further

• Use top-down design– Repeatedly split up the problem into smaller

sub problems– Solve the main task by solving each of the sub

problems


Algorithm design 2

• Structured programming is a strategy for solving problems

• A structured program is written using simple control structures. These define an algorithm

• A simple control structure is often a sequence, a selection or a repetition


A sequence

• A sequence consists of steps, performed one by one


A selection

• A selection contains a condition that can be evaluated to true or false

false true


A repetition

• A repetition repeats steps, as long as a condition is true

false

true


What is a programming language?

• A set of rules used to communicate an algorithm

• C is a procedural programming language– The traditional model– Specifies an explicit sequence of steps to follow

to obtain a result

February 2006 Basis-C-1/LL 14 Michael E. Caspersen, 2000 Gymnasieorientering 1.12

Milepæle i sprogudviklingen

Fortran

Algol

PascalSimula

C

C++

Smalltalk

Java

1960

1957

1967

1971

1980

1985

1995

Lisp

1958

FP

MirandaHaskell

Standard ML PrologBETA

Imperativesprog

Funktions-sprog

Logik-sprog


What is an imperative language?

• A program written in an imperative programming language is a collection of commands to the computer to perform certain operations– x:= x + 1

– write(”Restart Windows”)

– computeAverageSalary(totalSalary, nrOfPeople)

– rotate(something)


Procedural programmering

• Procedures are abstractions over commands• A programming style that uses commands

in certain control patterns• Models systems whose state changes as a

function over time • Every command has a measurable effect on

its environment• Assignment!!


From then till now

• Imperative programming languages are based on the von Neumann architecture (one type of architecture)

• Modern programming languages are based on an abstract, technology independent computation model


ANSI C

• American National Standards Institute ”C”– Very common C standard– Developed in 1989


C

• C is the result of the further development of earlier languages

• C is the basis for many newer languages (Concurrent C, C++, C#)

• Often called a middle level language – contains the building blocks that you need


Programming

• Define the problem

• Write algorithm that solves the problem

• Program the algorithm in C

• Test the program


• Programs have to be translated to the target computers machine language

– Compiler: the program that translates

– Source file: input to the compiler

– If the program is syntactically correct, the compiler will save the machine language instructions in an object file

• The linker combines an object file with already existing libraries of functions and procedures in an executable file

Programming 2


Programming 3

• Several steps:– Editor: used to make source code– Pre-processor: enhances with include files– Compiler: used to make object code– Linker: used to link object code and libraries– Run: used to load and execute a program


Programming 4

edit compile execute


Programming in C

• A C program consists of one or more source files, each containing parts of the program– Joint/common declarations are often collected

in header files


Hello World, once again/* The traditional first program in honour of Dennis Ritchie, who invented C while at Bell Labs in 1972.*/

#include <stdio.h>

int main(void)

{

printf("Hello, world!\n");

return 0;

}


#include <stdio.h> message to the preprocessor that the standard i/o library is to be included

int main(void)

{


return 0;

}


#include <stdio.h>

int main(void) the program starts at main

{


return 0;

}


#include <stdio.h>

int main(void)

{ a new function, identified by {


return 0;

}


#include <stdio.h>

int main(void)

{

printf("Hello, world!\n"); printf prints the text on the screen

return 0;

}


#include <stdio.h>

int main(void)

{


return 0; return 0 indicates correct termination

}


#include <stdio.h>

int main(void)

{


return 0;

} function complete, indicated by }


Example#include <stdio.h>

int main(void)

{

char c;

c = 'A';

printf("%c\n", c); /* the letter A is printed */

return 0;

}


Example 2

#include <stdio.h>

int main(void)

{

float x, y;

x = 1.0;

y = 2.0;

printf("The sum of x and y is %f.\n", x + y);

return 0;

}


#include <stdio.h>

int main(void)

{

char first, middle, last;

int age;

printf("Input your three initials and your age: ");

scanf("%c%c%c%d", &first, &middle, &last, &age);

printf("\nGreetings %c.%c.%c. %s %d.\n", first,

middle, last, "Next year your age will be", age + 1);

return 0;

}


/*This version allows white space to be typed between the initials on input.*/

#include <stdio.h>

int main(void)

{

char first, middle, last;

int age;

printf("Input your three initials and your age: ");

scanf("%c %c %c%d", &first, &middle, &last, &age);

printf("\nGreetings %c.%c.%c. %s %d.\n", first,

middle, last, "Next year your age will be", age + 1);

return 0;

}


#include <stdio.h>

#define PI 3.141592653589793

int main(void)

{

double radius;

printf("\n%s\n\n%s", "This program computes the area of a circle.", "Input the radius: ");

scanf("%lf", &radius);

printf("\n%s\n%s%.2f%s%.2f%s%.2f\n%s%.5f\n\n",

"Area = PI * radius * radius",

" = ", PI, " * ", radius, " * ", radius,

" = ", PI * radius * radius);

return 0;

}


/* Read in two integers and print their sum. */

#include <stdio.h>

int main(void)

{

int a, b, sum;

printf("Input two integers: ");

scanf("%d%d", &a, &b);

sum = a + b;

printf("%d + %d = %d\n", a, b, sum);

return 0;

}


How not to do it …int main(

){float qx,

zz,

tt;printf("gimme 3"

);scanf

( "%f%f %f",&qx,&zz

,&tt);printf("averageis=%f",(qx+tt+zz)/3.0);

return 0;}


#include <stdio.h>

int main(void)

{

int x, y, z, min;

printf("Input three integers: ");

scanf("%d%d%d", &x, &y, &z);

if (x < y)

min = x;

else

min = y;

if (z < min)

min = z;

printf("The minimum value is %d\n", min);

return 0;

}


Editing

• Create a text file using an editor – e.g. vi – containing a C program

• The file name has to end with .c, indicating that the file contains C source code

• E.g. test.c


Compiling

• gcc is the GNU C Compiler

• The gcc compiler is a tool used for converting text C source files to executable binary files

• gcc alternately calls the pre-processor, the compiler and the linker

• Errors at this point are called syntax errors or compile-time errors

.


Compiling 2

• Using compiler flags can help finding potential fatal errors in source code

• gcc test.c

– Gives an executable file called a.out

• gcc test.c -o test

– Gives an executable file called a.out test (instead of a.out)

• This allows for more readable file names ….


C program structure

Pre_processor instructions

main function heading{ declarations statements}


C standard libraries

• Libraries contain standard program modules (called functions)– E.g. math, standard input/output, string

manipulation– ANSI needs access to certain standard libraries– Each library has a standard file header, name

ending with .h


• As an example:– stdio.h (contains e.g. printf)– Can be used by writing– #include <stdio.h>

C standard libraries 2


Symbolic constants

• A symbolic constant is a name that is substituted for a sequence of characters

• #define is used to define constants and macros,– E.g. #define PI = 3.14


Comments

• /* this is a comment */

• Comments can span several lines

• Everything between /* and */ is ignored by the compiler


main

• main is the function that is called first• All other functions are called from main• Every C program must have a main function• int main(void)

– () after main means that it is a function– int describes the return type– void indicates that the function does not take

arguments


Statements

• A statement implies that a certain action is performed

• 3 different kinds in C– Expression statement– Compound statement– Control statement


Expression statements

• An expression statement consists of an expression followed by a semi colon

• The execution of such an expression implies the evaluation of the related expression

• E.g. a = 6; c = a + b; ; (empty statement)


Compound statements

• Consists of several individual statements enclosed by { }

• Whatever lies inside { } is to be interpreted as a single statement {

statement1;

statement2;

} (NOTE – no ;)


Control statements

• These control the flow of execution in a program or a function

• 2 kinds– Selection

• if, if-else, switch

– Repetition• for, while, do-while


Return statements

• Used to inform the operating system about program status

• return(b); is the general form

• return(0); indicates that the program has terminated correctly

• All other return values mean error!


printf

• Used to write data to standard output• printf(format_string, arg1, arg2 …)• format_string is a character string containing

formatting information• Each group consists of the symbol % and a series of

conversion characters indicating the type• E.g. d for int, c for char, f for float or double• (Note int is d, NOT i)


scanf

• Used to read data from standard input• scanf(format_string, &arg1, &arg2 …)• format_string is a character string containing

formatting information• Each group consists of the symbol % and a series

of conversion characters indicating the type• E.g. d for int, c for char, f for float or double• (Same as for printf)


scanf 2

• The & symbol indicates that the next variable has to be associated with a value

• & means address-of

• & tells scanf where to find the variables that need a value

• E.g. scanf(”%d%d”, &a, &b)


Example

#include <stdio.h>

int main(void){ int a, b, sum; printf(”Enter two integers: \n”); scanf(”%d%d”, &a, &b); sum = a + b; printf(%d + %d = %d\n”, a, b, sum); return(0);}


Example 2#include <stdio.h>void main(){ int i=1, sum=0; while (i<=10) { sum = sum + i; i = i + 1; } printf(”The sum is %d\n”,sum); return(0);}


Example 2#include <stdio.h> instruction to the pre-processorvoid main() main program{ int i=1, sum=0; a declaration while (i<=10) { sum = sum + i; a compound statement i = i + 1; } printf(”The sum is %d\n”,sum); return(0); return, indicates everything OK }

introduction to “programming in c” lone leth thomsen

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