Introduction to C

1
Introduction to C

• For the participants of
• Practical Course Scientific Computing and
  Visualization

2
Contents

• Getting Started the first program
• data input and result output
• compilation and execution
• Variables, expressions, types, functions
• Control program flow
• loops, conditional statements
• Arrays and pointers
• Standard C libraries
• Preprocessing
• Makefiles

3
Getting started C Program structure

• Any C programm consists of
• functions
• variables
• Functions consist of
• statements (abc, function call, etc.)
• Statements includes expressions builtwith
  operations (for example, arithmeticalexpressoins
  with , -, \, )

4
Getting Started Input and Output of Data

• include ltstdio.hgt
• main()
• int a, b, resultprintf(Input
  a,b\t)scanf(d,d,a,b)
  resultabprintf(d plus d is equal to d
  \n, a,b,result)

5
Getting Started Compilation

• In order to execute the programm, compile it
• with
• gcc filename
• The executable file a.out will be produced,
• start it with
• a.out

6
Operators and Expressions in C

• binary (-,,,/,,,)
• xy year 4 b true
• Unary (-,,,) int a2 int pointer_to_a
  a int b-a int sum pointer_to_a
  b
• postfix and prefix operators (,--)
• a2 ba ca

7
Variables and their Types

• There are following main types in C
• bool (1 byte)
• char (1 byte)
• int (4 bytes)
• long, short, signed, unsigned int (4, 8 bytes)
• float (4 bytes)
• double (8 bytes)
• void
• For example bool btrue long int a char
  c a a 232334

Memory
...
...
reserved for a
8
Types of Expressions and Casting

• The types of single variables schould be declared
  by programmer
• float f_number 3.141592 double
  d_number 3.14159265358 int i_number3
• Many operations cause automatic conversions of
  operands, in order to bring them to common
  type
• i_numberf_number -gt 6.141592 int -gt
  float
• sizeof(f_number d_number)8 float -gt
  double
• sizeof(f_number (float)d_number)4 double
  -gt float

9
Functions

• The function definition in Cret_type name
  (arg_type1 arg_name1, ...,arg_typeN argnameN)
  ...double parabola(double x)
  //declare the new variable, that will be returned
  return xxdouble f0 parabola(0)
  double f1 parabola(1)

10
Are functions computing arithmetic expressins
powerfull enough ?

• Now let us try to define the well-known factorial
  function in C. This
  function can be specified as follows

11
Flow control Conditional Statement

• To test logical conditions and make decisions use
  conditional statement IF-ELSEif (condition)
  ... Statemen_block1 ...else ...
  Statemen_block1 ... For example
  int f(int n) if ( ngt0 )
  return nf(n-1)
  else return 1
  

12
Loops While and For
int i 1int fac 1
for (init cond post) ...
for (i1 iltn i) facfaci
while (cond) ...
while (iltn) facfaci ii1
do ... while (cond)
do facfaci ii1 while (iltn)
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Arrays Vectors and Matrices
float x31,3,5 include ltmath.hgt float
vector_normsqrt(x1x1x2x2x3x3)
float matrix_trace A11A22A33
float A331,2,3, 3,2,1,
5,6,7
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Arrays Strings

• Strings can be represented in C as arrays of
  characters (type char)
• For example
• 
  Memory

char strhelloint i0 while(stri!\0)
printf(c\n, stri) i
15
Arrays Pointers
char strhelloint i0 while(stri!\0)
printf(c\n, stri) i
...
str
16
Arrays Pointers
...
str

• while(str!\0)printf(c\n,(str))

17
Indirection and Address Operators (, ) Examples

• int x1, y2, z10
• int ipx
• yip
• ip0
• ip z3

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Indirection and Address Operators (, ) Examples

• void swap (int a, int b)
• int tmpa
• ab
• btmp
• swap(a,b) // wrong
• Swap(a,b) // correct

19
Multidimensional Arrays Pointers to Pointers
float A331,2,3, 3,2,1,
5,6,7
A2 ...
A1
20
Multidimensional arrays
A2 ...
A1
for(i0ilt3i) for(j0jlt3j)
printf(f , yij) printf(\n)
21
Arrays Dynamic Programming
As another example, let us implement the
factorial calculation in a more efficient way.
The main idea is to reuse once calculated
results.We store them in an array.
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Arrays Dynamic Programming
int factorial(int n)int res1 for(in igt0
i--) // has the result been //
already computed ? if(resultsi0)
resresi resultsires else
return resultsi return fac
23
Memory allocation

• C provides a number of functionsto allocate
  memory to store data instdlib.h
• void malloc(unsigned int nbytes)
• void free(void ap)

24
Memory allocation

• includeltstdlib.hgt
• int results
• main() resultsmalloc(100sizeof(integer))
  factorial(3)factorial(44)
• factorial(100)free(results)

25
Preprocessing

• File inclusion
• include ltfilenamegt
• include filename
• Macro substitutions
• define max(A,B) (A)gt(B) ? (A)(B)
• define CONSTANT 25
• Conditional inclusion
• ifndef __HELPER_H__define __HELPER_H__...en
  dif

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Standard libraries

• stdio.h
• standard input and output
• printf, scanf, fprintf, fscanf, fopen, flcose,
  ...
• string.h
• string processing
• Strlen, strcpy, strcat, strcmp, ...

27
Standard libraries

• stlib.h
• memory allocation, random numbers,type
  conversion
• atof, atoi, rand, alloc, malloc, free
• math.h
• mathematical functions
• sin, cos, sqrt, strcmp, remainder,...

28
Compilation with makefiles

• Makefiles consist of
• macro definitions
• rules of compilation
• dependences declaration

29
Compilation with makefiles
CCgcc CFLAGS -Wall pedantic OBJ helper.o
init.o boundary.o uvp.o main.o all (OBJ)
(CC) (CFLAGS) o sim (OBJ) lm clean rm
(OBJ) helper.o helper.h init.o helper.h
init.h ....