Page 79 - DCAP605_ADVANCED_DATA_STRUCTURE_AND_ALGORITHMS

Advanced Data Structure and Algorithms

Notes return (n * y);
}
How are we to define the data area for this function? It must contain the parameter n and the

local variables x and y. As we shall see, no temporary variables are needed. The data area must
also contain a return address. In this case, there are two possible points to which we might want
to return: the assignment of fact(x) to y, and the main program that called fact. Suppose that we
had two labels and that we let the label label2 be the label of a section of code.
Label 2: y = result;
within the simulating program. Let the label 1 be the label of a statement

Label 1: return(result);

This reflects a convention that the variable to result contains the value to be returned by an
invocation of the fact function. The return address will be stored as an integer i (equal to either 1
or 2). To effect a return from a recursive call the statement
switch(i) {
case 1: goto label1;
case 2: goto 1abe12;
}
is executed. Thus, if i = = 1. a return is executed to the main program that called fact, and if
i == 2, a return is simulated to the assignment of the returned value to the variable y in the
previous execution of fact.
Proving Correctness of Parenthesis in an Expression

Lab Exercise This program takes one mathematical expression and checks whether the
opening and closing parenthesis match or not.
#define LEFTBRACKET ‘{‘
#define RIGHTBRACKET ‘}‘
#include <stdio.h>
main()
{
char t, *p, expr[100];
printf(“Enter an expression :”);
scanf(“%s”,expr);
p=expr;
while(p != ‘\0’)
{
if( *p == LEFTBRACKET) push(p);
if(*p == RIGHTBRACKET) t=pop();
if(t < 0) (printf(“ERROR:”));
p++;
}

74 LOVELY PROFESSIONAL UNIVERSITY