1. Introduction to “Programming in C”
Lone Leth Thomsen

2. Contents Introduction to the course Mini project/evaluation
Purpose, literature
Mini project/evaluation
Today’s topics (easy start)
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3. 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
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4. Practical info Lectures Thursday 8.15 - 10.00
Exercises Thursday
10 modules, SE course
8 lectures with exercises
2 modules used on larger exam exercise
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5. 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
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6. 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
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7. 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
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8. 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
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9. 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
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10. A sequence A sequence consists of steps, performed one by one
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11. A selection
A selection contains a condition that can be evaluated to true or false
false
true
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12. A repetition
A repetition repeats steps, as long as a condition is true
false
true
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13. 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
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15. 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)
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16. 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!!
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17. 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
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18. ANSI C American National Standards Institute ”C”
Very common C standard
Developed in 1989
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19. 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
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20. Programming Define the problem Write algorithm that solves the problem
Program the algorithm in C
Test the program
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21. Programming 2
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
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22. 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
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23. Programming 4
edit
compile
execute
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24. 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
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25. 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; }
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26. 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) {
printf("Hello, world!\n");
return 0; }
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27. #include <stdio.h>
int main(void) the program starts at main {
printf("Hello, world!\n");
return 0; }
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28. #include <stdio.h>
int main(void)
{ a new function, identified by {
printf("Hello, world!\n");
return 0; }
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29. #include <stdio.h>
int main(void) {
printf("Hello, world!\n"); printf prints the text on the screen
return 0; }
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30. #include <stdio.h>
int main(void) {
printf("Hello, world!\n");
return 0; return 0 indicates correct termination }
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31. #include <stdio.h>
int main(void) {
printf("Hello, world!\n");
return 0;
} function complete, indicated by }
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32. Example #include <stdio.h> int main(void) { char c; c = 'A';
printf("%c\n", c); /* the letter A is printed */
return 0; }
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33. Example 2 #include <stdio.h> int main(void) { float x, y;
printf("The sum of x and y is %f.\n", x + y);
return 0; }
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34. #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; }
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35. #include <stdio.h>
/*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; }
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36. #include <stdio.h>
#define PI
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; }
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37. } /* 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; }
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38. 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;}
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39. #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; }
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40. 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
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41. 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
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42. 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 ….
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43. C program structure Pre_processor instructions main function heading {
declarations
statements }
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44. 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
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45. C standard libraries 2 As an example: stdio.h (contains e.g. printf)
Can be used by writing
#include <stdio.h>
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46. 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
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47. Comments /* this is a comment */ Comments can span several lines
Everything between /* and */ is ignored by the compiler
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48. 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
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49. Statements A statement implies that a certain action is performed
3 different kinds in C
Expression statement
Compound statement
Control statement
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50. 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)
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51. Compound statements
Consists of several individual statements enclosed by { }
Whatever lies inside { } is to be interpreted as a single statement {
statement1;
statement2;
} (NOTE – no ;)
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52. 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
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53. 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!
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54. 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)
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55. 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)
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56. 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)
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57. 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); }
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58. 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);
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59. Example 2 #include <stdio.h> instruction to the pre-processor
void 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
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