1. Elements of Programming Languages

2. Elements of Programming Languages
Outlines
Structures of programming languages
Values, types, and variables
Commands
Function calls
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Elements of Programming Languages

3. Structures of programming languages
Syntax and semantics
Classes of languages
Language processors
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Elements of Programming Languages

4. Structures of programming languages
Syntax: the form of programs
how expressions, commands, declarations, and other constructs must be arranged to make a well-formed program.
Semantics: the meaning of programs
how a well-formed program may be expected to behave when executed on a computer.
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5. Structures of programming languages
Classes of Languages
Imperative languages: C, Pascal, Java
Object-oriented languages: C++, Java
Concurrent languages: ADA, Modula
Functional languages: Lisp, Haskell
Logic languages: Prolog
Language processors
Compiler
Interpreter
Hybrid
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6. Elements of Programming Languages
Example Program
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4;j++)
d[k++]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res+=inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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Elements of Programming Languages

7. Values, types and variables
Primitive values/types
Composite values/types
Expressions
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Elements of Programming Languages

8. Elements of Programming Languages
Use of values
A value is any entity that can be manipulated by a program.
evaluated
stored
passed (sent) to different parts of programs
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9. Elements of Programming Languages
Types of values
Different programming languages support different types of values
C : integers, real numbers, structures, arrays, pointers
C++ : integers, real numbers, structures, arrays, pointers, objects.
JAVA : booleans, integers, real numbers, arrays, and objects.
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Elements of Programming Languages

10. Primitive types/values
A primitive value cannot be decomposed into simpler values.
A primitive type is one whose values are primitive.
Built-in primitive types
C, C++
integers, reals, characters, pointers.
JAVA
booleans, integers, reals, characters.
Defined primitive types
C : structures, arrays.
C++ : structures, arrays, objects.
JAVA : arrays, and objects
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Elements of Programming Languages

11. Built-in primitive types/values
Boolean type
false and true.
Character type
‘A’, ‘+’, ‘1’, ‘.’
Integer type
121, , 0
Float type
, , .9801E-908
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12. Elements of Programming Languages
Literals
denote a fixed value of some type
Examples:
Integers: 345,
Floats: , E-21
Booleans: TRUE, FALSE
Characters: ‘3’, ‘a’, ‘+’, ‘\0’ (null)
Strings: “This is a string.”
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13. Elements of Programming Languages
Example of literals
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4;j++)
d[k++]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res+=inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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Elements of Programming Languages

14. Composite types/values
A composite value (or data structure) can be composed into simpler values.
A composite type is a type whose values are composite.
Examples:
Arrays
Collections of values of the same type
Refer to by the index
Structures, and records
Collections of values of many types
Refer to by name
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15. Elements of Programming Languages
Arrays
3.21
4.44
6.09
9.12
0.96
{3.21, 4.44, , 0.96} 3 4 6 9 -2 -5 1 2
-10
-11 5 -4 8 1 2 3 4 C A N
{‘C’, ‘A’, ‘N’}
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16. Elements of Programming Languages
Records
name: string
address: string
ID: integer
phone: string
gpax: float
{“john”, “12 Phayathai Bangkok”,
, “ ”, 3.2}
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17. Elements of Programming Languages
Variables
Containers of values
Have names
Are of some types
Simple
composite
Example:
int credit=3, age=18;
float gpax=3.12, fee= ;
char grade=‘A’;
char name[30]=“john”; /* string */
int score[5][50];
array
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18. Elements of Programming Languages
Example of variables
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4;j++)
d[k++]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res+=inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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19. Elements of Programming Languages
Constructions
Construction
expression that constructs a composite value from its component values
Array constructor
{10, 41, -7, 0, 9}
Structure constructor
{“somchai”, “1/2 Phayathai Bangkok”, , “ ”, 3.1}
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20. Example of array constructors
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4;j++)
d[k++]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res+=inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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Elements of Programming Languages

21. Elements of Programming Languages
Expressions
Expression
evaluated to yield a value.
Expressions may be formed in various ways. In this section we shall survey the fundamental forms of expression:
Constant
Variables
Constructions
Function calls
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22. Example of expressions
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4;j++)
d[k++]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res=res+inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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23. Elements of Programming Languages
Function calls
Function call
computes a result by applying a part of program called “function” or “method” to one or more arguments.
A function call F (E1, ,En)
F : the name of the function
E1, ,En : the arguments in the form of expressions.
Example: sqrt(2), sin(.23), pow(3.2, 3)
An operator may be thought of as denoting a function.
unary operator: -3, ~TRUE
binary operator: (3+4)/5+6, 56%10
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24. Example of function calls
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4;j++)
d[k++]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res=res+inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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Elements of Programming Languages

25. Elements of Programming Languages
Commands
Assignments
Sequential commands
Jumps
Conditional commands
Iterative commands
Proper procedure calls
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26. Elements of Programming Languages
Assignments
variable = expression
Find the value from the expression
Store the value in the variable
Ex: average = x+y+z/3;
variable++, variable--
Meaning: variable =variable+1 (or -1)
Ex: i++; /* i=i+1 */
i--; /* i=i-1 */
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27. Elements of Programming Languages
Assignments
Variable initialization
type variable = literal;
Store the value of literal in the variable
Ex: float average = 0;
int day[7]={1,2,3,4,5,6,7};
char name[30]=“mary”;
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28. Example of assignments
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4; j++)
d[ k++ ]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res=res+inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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29. Elements of Programming Languages
Sequential Commands
Unless stated otherwise in your program, after finishing executing an command/instruction, the next command/instruction is executed.
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30. Elements of Programming Languages
Jumps
Indicate the next instruction to be executed.
goto label
Ex: loop: x=x+1;
y=y*2;
goto loop;
printf(“never get here!!!”);
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31. Elements of Programming Languages
Conditional Commands
If statement
if (condition)
then-part
[else
else-part] else-part is optional
When condition is true, then-part is executed.
Otherwise, else-part is executed.
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32. Example of if statements
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4; j++)
d[k++]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res=res+inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
if(x1>x2) {dx=x1-x2; …}
else {dx=x2-x1; …}
if (y1>y2) dy=y1-y2;
else dy=y2-y1;
return(sqrt(dx*dx+dy*dy));
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33. Elements of Programming Languages
Iterative Commands
While loop
Do-while loop
For loop
for (initial-st ; condition ; incr-st )
loop-body
Ex: factorial=1;
for (i=1; i<10; i++)
{ factorial=factorial*i;
printf(“%d ! =%d\n”, I, factorial); }
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34. Elements of Programming Languages
Example of iteratives
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4; j++)
d[k++]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res=res+inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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Elements of Programming Languages

35. Elements of Programming Languages
Functions
Function prototype
Function definition
Function call
Local/Global variables
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36. Elements of Programming Languages
Function prototype
Function name
Return type
Arguments
Examples:
float average(int a, int b, int c);
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37. Example of function prototypes
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4; j++)
d[ k++ ]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res=res+inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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38. Elements of Programming Languages
Function Definition
Function header
Similar to function prototype
Function body
Variable declaration
Sequence of commands
Example
real average(int a, int b, in c)
{ int sum;
sum=a+b+c;
return sum/3; }
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39. Example of function definition
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4; j++)
d[ k++ ]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res=res+inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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40. Elements of Programming Languages
Function call
Function name
List of arguments/parameters
Example:
x=average(9, 5, -1);
The value in x is (9+5+(-1))/3
aav=average(9, 5, average(2,-1, 8));
The value in aav is (9+5+(2+9-1)+8)/3) /3
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41. Example of function calls
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4; j++)
d[k++]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res=res+inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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42. Global/local variables
Global variables
Variables which can be used at any location in a program.
Local variables
Variables which can be used locally in a function.
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43. Example of local variables
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4;j++)
d[k++]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res=res+inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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44. Parameters/arguments
Copy parameter mechanisms
Reference parameter mechanisms
The Correspondence Principle
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45. Elements of Programming Languages
Example of parameters
float mean(float inp[], int s);
float distance(float x1,
float y1,
float x2,
float y2);
int main(int argc, char *argv[])
{ float x[4]={2,1,6,0};
float y[4]={1,3,1,4};
float d[6];
int i,j,k=0;
for (i=0;i<4;i++)
for (j=i+1; j<4; j++)
d[k++]=
distance(x[i],y[i],x[j],y[j]);
printf("The mean is %f\n",
mean(d, 6));
system("PAUSE");
return 0; }
float mean(float inp[],
int s)
{ int i;
float res=0;
for (i=0; i<s; i++)
res=res+inp[i];
return res/s; }
float distance(float x1,
float y1,
float x2,
float y2)
{int dx,dy;
dx=abs(x1-x2);
dy=abs(y1-y2);
return(sqrt(dx*dx+dy*dy));
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