Thursday, December 28, 2006

One of the main causes of the fall of the Roman Empire was that,

lacking zero, they had no way to indicate successful termination of

their C programs.

- Robert Firth

TutorialReferences on website.

bool p;

// some statements here

if (p) and if (true == p)

if (!p) and if (false == p)

double area, circumference, volume, radius=7.5;//circlearea = 3.1415 * radius * radius;circumference = 2 * 3.1415 * radius;cout<<area<<" "<<circumference<<endl;//spherearea = 4.0 * 3.1415 * radius * radius;volume = 4.0/3.0 * 3.1415 * radius * radius * radius;cout<<area<<" "<<volume<<endl;

double area, circumference, volume, radius=7.5;//circlearea = 3.1415 * radius * radius;circumference = 2 * 3.1415 * radius;cout<<area<<" "<<circumference<<endl;//spherearea = 4.0 * 3.1415 * radius * radius;volume = 4.0/3.0 * 3.1415 * radius * radius * radius;cout<<area<<" "<<volume<<endl;

Avoid magic numbers

double PI = 3.14159;double area, circumference, volume, radius=7.5;//circlearea = PI * radius * radius;circumference = 2 * PI * radius;cout<<area<<" "<<circumference<<endl;//spherearea = 4.0 * PI * radius * radius;volume = 4.0/3.0 * PI * radius * radius * radius;cout<<area<<" "<<volume<<endl;

//Better but still not good enoughdouble PI = 3.14159;double area, circumference, volume, radius=7.5;//circlearea = PI * radius * radius;circumference = 2 * PI * radius;cout<<area<<" "<<circumference<<endl;//spherearea = 4.0 * PI * radius * radius;volume = 4.0/3.0 * PI * radius * radius * radius;cout<<area<<" "<<volume<<endl;

const double PI = 3.14159;double area, circumference, volume, radius=7.5;//circlearea = PI * radius * radius;circumference = 2 * PI * radius;cout<<area<<" "<<circumference<<endl;//spherearea = 4.0 * PI * radius * radius;volume = 4.0/3.0 * PI * radius * radius * radius;cout<<area<<" "<<volume<<endl;

#define PI 3.14159

At file scope: before main()

FunctionsCall by Value

The Black Box Analogy

A black box refers to something that we know how to use, but the method of operation is unknown

A person using a program does not need to know how it is coded

A person using a program needs to know what the program does, not how it does it

Functions and the Black Box Analogy A programmer who uses a function

needs to know what the function does, not how it does it

A programmer needs to know what will be produced if the proper arguments are put into the box

int sum(int x, int y);int main(){ int answer;cout<<“In main”;answer = sum(2,3);cout<<answer;

return 0;}int sum (int x, int y){int z=x+y;cout<<“In sum”;return z;

}

int sum(int x, int y);int main(){ int answer;cout<<“In main”;answer = sum(sum(5,6),3);cout<<answer;

return 0;}int sum (int x, int y){int z=x+y;cout<<“In sum”;return z;

}

Larger of two numbers

header files

•predefined functions #include <math.h>

Math library

#include <math.h>

sin(x), cos(x), tan(x), asin(x), acos(x), atan(x), sinh(x), cosh(x), tanh(x), exp(x), log(x), log10(x), pow(x,y), sqrt(x), ceil(x), floor(x)

int main(){ int num; double sine_val; for(num=1; num < 100; num++) { sine_val = sin(num*3.14/180.0); cout << num <<" "<<sine_val<< "\n"; }

return 0;}

#include <stdlib.h>

int rand(void)

#include <ctype.h>int isalpha(char c);int isdigit(char c);int isalnum(char c);int ispunct(char c);int isspace(char c);int islower(char c);int isupper(char c);int tolower(char c);int toupper(char c);

Example of local variablesint example(int x){ x=54; return x;}

int main(){int x=23;cout<<x<<"\n"; example(x);cout<<x<<"\n";

x=example(x);cout<<x<<"\n"; return 0;

}

int example(int x){ x=54; return x;}

int main(){int x=23;cout<<x<<"\n"; //prints 23example(x);cout<<x<<"\n"; //prints 23x=example(x);cout<<x<<"\n"; //prints 54return 0;

} return value example

Variables declared outside of all functions: global variables

Global variables hold their value throughout the lifetime of your program

Example of global variables

int global=100;

void example(int x){ global=10*x;}

int main(){cout<<global<<"\n"; global = 200;cout<<global<<"\n"; example(3);cout<<global<<"\n"; example(global); cout<<global<<"\n"; return 0;

}

Example of global variables

int global=100;

void example(int x){ global=10*x;}

int main(){cout<<global<<"\n"; //prints 100global = 200;cout<<global<<"\n"; //prints 200example(3);cout<<global<<"\n"; //prints 30example(global); cout<<global<<"\n"; //prints 300

return 0;}

Use of global variables can have unexpected effects.

Software engineering principles

local variables - life of functionglobal variables - existence of entire

execution of programGlobal variables are initialized at start of

program. They are given a value of zero if no other initialization value is specified.

Un-initialized local variables will have unknown values

Local variables are associated with the block they are declared in.

int a=3;

if(a<=3){

int x=4;

cout<<x;

}

Swap example

What is wrong here?

int a=3;

if(a<=3){

int x=4;

cout<<x;

}

cout<<x;

Local variables are associated with the block they are declared in.

int a=3;

if(a<=3){

int x=4;

cout<<x;

}

cout<<x; //Error

int a=10; //global variable

int main(){

int a=20;

cout<<a<<endl;

return 0;

}

int a=10; //global variable

int main(){

int a=20;

cout<<a<<endl; //prints 20

return 0;

}

We can use scope resolution operator :: to access global variables.

int a=10; //global variable

int main(){

int a=20;

cout<<a<<endl;

cout<<::a<<endl;

return 0;

}

int a=10; //global variable

int main(){

int a=20;

cout<<a<<endl; //prints 20

cout<<::a<<endl; //prints 10

return 0;

}

int a=10;

int doSomething(){ int a=30; cout<<a<<endl; return a;}

int main(){int a=20;cout<<a<<endl; cout<<::a<<endl; cout<<doSomething()<<endl; return 0;

}

int a=10;

int doSomething(){ int a=30; cout<<a<<endl; //prints 30 return a;}

int main(){int a=20;cout<<a<<endl; //prints 20cout<<::a<<endl; //prints 10cout<<doSomething()<<endl; //prints 30return 0;

}

What will happen here?

void example(int f){int f; f=3;cout<<f;

}

What will happen here?

void example(int f){int f; //Error:redefinition of formal parameter ff=3;cout<<f;

}

List of marksList of names…

Arrays offer a convenient means of grouping together several related variables

Arrays

Declaring an array

type array_name[size]; allocates memory for size variables index of first element is 0 index of last element is size-1 size must be a constant