Page 156 - DCAP201_FUNDAMENTALS_OF_DATA_STRUCTURES

Unit 9: Stacks

int parenthesischecker(char str[]) Notes
{
struct stack s;
char ch;
int i,flag=0;/*0 for no error, 1 for error*/
s.top=-1;
for(i=0;((str[i]!=’’) && (flag==0));i++)
{if(str[i]==’(‘)
push(&s,str[i]);
else
{ch=pop(&s);
if(ch!=’(‘)
flag=1;
}
}
if(s.top!=-1)
flag=1;
return flag;
}
void main()
{
char str[MAX],flag;
clrscr();
printf(“nEnter a string of parenthesis?”);
gets(str);
flag=parenthesischecker(str);
if(flag==0)
{printf(“nParenthesis Match O.K.”);
}
else
{printf(“nOpening/Closing Parenthesis do not match.”);
}
getch();
}

9.5.2 Evaluation of Arithmetic Expressions

Stacks are useful in evaluation of arithmetic expressions. Consider the expression

5 * 3 +2 + 6 * 4
The expression can be evaluated by first multiplying 5 and 3, storing the result in A, adding
2 and A, saving the result in A. We then multiply 6 and 4 and save the answer in B. We finish off
by adding A and B and leaving the final answer in A.

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