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//Solved Example 3.3:
//Convering an infix expression to a Postfix Expression:
function[sta]=push(stac,ele)
sta=0;
if(stac.top==0)
stac.a=ele;
stac.top=stac.top+1;
else
stac.a=[stac.a(:,:) ele]
stac.top=stac.top+1;
end
disp(stac);
sta=stac;
endfunction
function[ele,sta]=pop(stack)
ele='-1';
if(stack.top==0)
disp("Stack Underflow");
break;
else
ele=stack.a(stack.top);
stack.top=stack.top-1;
if(stack.top~=0)
b=stack.a(1);
for i2=2:stack.top
b=[b(:,:) stack.a(i2)];
end
stack.a=b;
else
stack.a='0';
end
end
sta=stack;
endfunction
function[l]=strlen(x)
i=1;
l=0;
[j,k]=size(x)
for i=1:k
l=l+length(x(i));
end
endfunction
function[p]=pre(s1,s2)
i1=0;
select s1,
case '+' then i1=5;
case '-' then i1=5;
case '*' then i1=9;
case '/' then i1=9;
end
i2=0;
select s2,
case '+' then i2=5;
case '-' then i2=5;
case '*' then i2=9;
case '/' then i2=9;
end
p=0;
p=i1-i2;
if(s1=='(')
p=-1;
end
if(s2=='('&s1~=')')
p=-1;
end
if(s1~='('&s2==')')
p=1;
end
endfunction
function[a2]=intopo(a1,n)
stack=struct('a',0,'top',0);
l1=1;
l2=strlen(a1(1))
for i=2:n
l2=l2+strlen(a1(i))
end
a2=list();
while(l1<=l2)
symb=a1(l1);
if(isalphanum(string(a1(l1))))
a2=list(a2,symb);
else
while(stack.top~=0&(pre(stack.a(stack.top),symb)>=0))
[topsymb,stack]=pop(stack);
if(topsymb==')'|topsymb=='(')
a2=a2;
else
a2=list(a2,topsymb);
end
end
if(stack.top==0|symb~=')')
stack=push(stack,symb);
else
[ele,stack]=pop(stack);
end
end
l1=l1+1;
end
while(stack.top~=0)
[topsymb,stack]=pop(stack);
if(topsymb==')'|topsymb=='(')
a2=a2;
else
a2=list(a2,topsymb);
end
end
disp(a2);
endfunction
//Calling Routine:
a1=['(' '2' '+' '3' ')' '*' '(' '5' '-' '4' ')']
a2=intopo(a1,11)
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