1. Slide 1 Chapter 5-b Attributes of variables

2. Slide 2 Attributes of variables { int sum = 5;... } sum int 0000 0000 0000 0101 IdentifierType Value 0110 0010 Address Storage Symbol Table

3. Slide 3 Variable Names sum=0.0 DO I = 1 TO 10 sum = sum + i END DO... t = SQR(SUM)... FUNCTION sqr(val) val = val*val RETURN VAL Names: Fortran is not case sensitive. Type: Fortran allows implicit declarations.

4. Slide 4 Naming Conventions public void actionPerformed (ActionEvent e){ int value = Math.PI;... } Method names start with lower case Class names start with upper case Constants are all upper case Local variables are all lower case

5. Slide 5 Aliasing: Variables union { short i; float f; char c; } uval; c i f uval Aliasing using variables is meant for conserving storage space.

6. Slide 6 Aliasing: Pointers int i; int *p=&i; char *c; c=(char*)p; p c i Aliasing using pointer variables is not meant for conserving storage space.

7. Slide 7 Static Variables (Fortran) SUBROUTINE fun() DATA k/0/ K=K+1 PRINT *, K RETURN Call statementOutput CALL FUN() 1 CALL FUN() 2 CALL FUN() 3 CALL FUN() 4... In Fortran, all variables are by default static

8. Slide 8 Static Variables (C) void fun(){ int k=0; k++; printf(“\n %d”,k); } Call statementOutput fun( ); 1... fun( ); 1 fun( ); 2 fun( ); 3 fun( ); 4... void fun(){ static int k=0; k++; printf(“\n %d”,k); }

9. Slide 9 Stack Dynamic Variables i i ji { int i;... { int j;... }... }

10. Slide 10 Recursion n=3 n=2 n=3 n=2 n=1 n=3 n=2 1 n=3 2 6 3 int fact (int n){ if(n==1) return 1; else return n*fact(n-1); } 2 int fact (int n){ if(n==1) return 1; else return n*fact(n-1); } 1 int fact (int n){ if(n==1) return 1; else return n*fact(n-1); }

11. Slide 11 Heap-Dynamic Variables (1) int size=100; int *p; p = (int *) malloc(size*2);... free(p); 0 99 p p Heap allocation requires effective memory management ????

12. Slide 12 Heap-Dynamic Variables (2) int *node; node = new int; //Allocates an int cell.... delete node; //free the allocated memory. C++ Stack s = new Stack(); Java

13. Slide 13 Scope (C) int x;... main(){ int k;... { int k;... }... } Global variable Local variable

14. Slide 14 Scope (Java) public float fun(){ int[] x = {10, 20, 30}; float sum=0; for (int i=0; i<3; i++){ sum=sum+x[i]; } System.out.println(“Sum=”+sum); float v; v=sum/2; return v; } Local variables

15. Slide 15 Scope (Java classes) public class Myclass{ public void add(int y){ x = x+y; } int x=10; } Java allows the above type of declaration of instance variables but it is not advised.

16. Slide 16 Scope Vs. Lifetime (1) void compute() { static int k;... } Scope of the variable is limited to the function block, while its lifetime is the same as the total program execution time.

17. Slide 17 Scope Vs. Lifetime (2) void compute() { int value;... printinfo();... } void printinfo(){... } Scope of “value” does not extend to the function “printinfo”, but lifetime of value does.