Software Engineering. Dr Ian Reid B4, 4 lectures, Hilary Term. http://www.robots.ox.ac.uk/~ian/Teaching/SoftEng. Software Engineering vs structured programming. Not really a course about software engineering… Software engineering Mostly about concepts, Structured programming
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http://www.robots.ox.ac.uk/~ian/Teaching/SoftEng
Software Engineering vs structured programming
The Role of Computing in Engineering
some examples…
Software engineering versus programming
Software vs “other” engineering
Out
+

Modularity: Opamp buffer
Software vs “other” engineering
Intrinsic difficulties with software
When software projects go wrong
When software projects go wrong
NHS National programme for IT: NPfIT
Algorithms
Data structures
Programs
state
thrust
Simulator
state
Display
Data flows
Implementation in Matlab and C
N= 10;
tot = 0;
totsq = 0;
for i=1:N
tot = tot+i;
totsq = totsq+i^2;
end
tot
totsq
int i;
int tot = 0;
int totsq = 0;
for (i=1; i<N; i++) {
tot += i;
totsq += i*i;
}
cout << tot << endl;
cout << totsq << endl;
Organisation of Matlab programs
Source code
Source code
…..
.c .cc
.c .cc
compilation
compilation
Object file
Object file
…..
.o
.o
linking
executable
% compute factorial
function z = fact(n)
% function body
z = 1;
for i=1:n
z = z*i;
end
// compute factorial
int fact(int n)
{
int i, val = 1;
for (i=1; i<=n; i++) {
val *= i;
}
return val;
}
fact(10)
a = 6;
z = fact(a);
[V,D] = eig(A);
myexp.h file
float myexp(float x);
myexp.c file
float myexp(float x)
{
const float precision = 1.0e6;
float term=1.0, res=0.0;
int i=0;
while (fabs(term)>precision) {
res += term;
i++;
term = pow(x,i)/fact(i);
}
return res;
}
Input parameters
Hidden input
Output values
Input parameters
Hidden output
Function encapsulationLowlevel implementation of function call
Memory
CODE
machine code
DATA
global variables
local variable m
…
local variable 1
return location
parameter x
…
Activation
record
parameter 1
return value n
STACK
…
return value 1
int i=5, j=10;
swap(i,j);
cout << i << “ “ << j << endl;
Pass by value
Pass by reference
void swap(int a, int b)
{
int temp = a;
a = b;
b = temp;
return;
}
void swap(int& a, int& b)
{
int temp = a;
a = b;
b = temp;
return;
}
class Complex {
public:
double re, im;
};
int i;
Complex z;
Class definition
Create a variable (an instance) of this type
state
thrust
Simulator
state
Display
Example: VTOL stateclass State {
double pos, vel, mass;
bool landed;
};
State s;
s.pos = 1.0;
s.vel = 20.0;
s.mass = 1000.0;
s.landed = false;
s.pos = s.pos + s.vel*deltat;
Thrust = ComputeThrust(s);
In Matlab introduce structure fields without declaration
s.pos = 1.0;
s.vel = 20.0;
…
Thrust = ComputeThrust(s);
Accessing class membersImage ReadImage(const string filename, bool& flag);
bool ReadImage(const string filename, Image& im);
function [Image, errflag] = ReadImage(filename)
int a[10];
res = a[0] + a[1] + a[2];
Complex z[20];
State s[100];
for (t=1; t<100; t++) {
s[t].pos = s[t1].pos + s[t1].vel + 0.5*g;
s[t].vel = s[t1].vel + g – GetThrust(s[t1], burnrate)/s[t1].mass;
s[t].mass = s[t1].mass – burnrate*escapevel;
}
double d[10][5];
has elements:
d[0][0] d[0][1] … d[0][4]
.
.
.
d[9][0] d[9][1] … d[9][4]
class Complex {
public:
double re, im;
double Mag() {
return sqrt(re*re + im*im);
}
double Phase() {
return atan2(im, re);
}
};
Complex z;
cout << “Magnitude=“ << z.Mag() << endl;
{ re = x; im = y; }
class Complex {
public:
Complex(double x, double y) { re=x; im=y; }
double Re() { return re; }
double Im() { return im; }
double Mag() { return sqrt(re*re + im*im);}
double Phase() { return atan2(im, re);
}
private:
double re, im;
};
Complex z(10.0,8.0);
cout << “Magnitude=“ << z.Mag() << endl;
cout << “Real part=“ << z.Re() << endl;
class Complex {
public:
Complex(double x, double y) {
r = sqrt(x*x + y*y);
theta = atan2(y,x);
}
double Re() { return r*cos(theta); }
double Im() { return r*sin(theta); }
double Mag() { return r;}
double Phase() { return theta; }
}
private:
double r, theta;
};
Complex z(10.0,8.0);
cout << “Magnitude=“ << z.Mag() << endl;
cout << “Real part=“ << z.Re() << endl;
class Complex {
public:
Complex(double x, double y);
double Re();
double Im();
double Mag();
double Phase();
private:
double re, im;
};
C++ program organisation#include “Complex.h”
Complex::Complex(double x, double y) {
re = x; im = y;
}
double Complex::Re() { return re; }
double Complex::Im() { return im; }
double Complex::Mag() {
return sqrt(re*re+im*im);
}
double Complex::Phase() { return atan2(im,re); }
C++ program organisationclass A : public B {
…
};
Data: width, height
posx, posy
Methods: raise(), hide()
select(), iconify()
class TextWindow
class GraphicsWindow
Data: cursor_x, cursor_y
Data: background_colour
Methods: redraw(), clear()
backspace(), delete()
Methods: redraw(), clear()
fill()
class InteractiveGraphicsWindow
Data:
Methods: MouseClick(), MouseDrag()
Exampleclass Window {
…
virtual void redraw();
};
virtual void func() = 0;
then A has no implementation of func()
for (int i=0; i<N; i++) {
obj[i]>Draw();
}
class BoundedArray {
public:
float GetElement(int i) {
if (i<0  i>=10) {
cerr << “Access out of bounds\n”;
return 0.0;
} else {
return a[i];
}
}
private:
float a[10];
};
template <class Type>
class BoundedArray {
public:
Type GetElement(int i) {
if (i<0  i>=10) {
cerr << “Access out of bounds\n”;
return Type(0);
} else {
return a[i];
}
}
private:
Type a[10];
};
BoundedArray<int> x;
BoundedArray<Complex> z;
#include<vector>
int main() {
std::vector<int> v;
for (int i=0; i<20; i++) v.push_back(i);
for (int i=0; i<v.size(); i++)
std::cout << v[i] << std::endl;
}
int size;
std::vector<Complex> z;
std::cin >> size;
z.resize(size);
z[5] = Complex(2.0,3.0);
int width, height;
std::vector< std::vector<int> > x;
x.resisze(height);
for (int i=0; i<height; i++)
x[i].resize(width);
x[2][3] = 10;
…
std::vector<int> v;
std::vector<int>::iterator i;
for (it=v.begin(); it!=v.end(); it++) …
class Cell {
public:
Cell();
bool Visited();
void MarkVisited();
bool BottomWall();
bool RightWall();
void BreakBottom();
void BreakRight();
private:
bool bottomwall;
bool rightwall;
bool visited;
};
class Maze {
public:
Maze(int width, int height);
void Compute(int x, int y);
void Print();
private:
int Rand(int n);
int H, W;
std::vector< std::vector<Cell> > cells;
};
int main(int argc, char* argv[])
{
int width, height;
cerr << "Enter maze width: ";
cin >> width;
cerr << "Enter maze height: ";
cin >> height;
Maze m(width, height);
m.Compute(height1,0);
m.Print();
return 0;
}