The following is the error in my program :


lab1.cpp:80: error: ISO C++ forbids comparison between pointer and integer


Here is my program...

//Convert an infix expression to postfix expression...

#include<iostream>
#include<string>
#include<cstdlib>
using namespace std;
char ifx[50],pfx[50],stk[50];
int top=-1,n;
void push(char ch)
{
if(top!=n)
{
ch=stk[top];
top++;
cout<<"\nElement added was "<<ch;
}
else
cout<<"\nThe stack is full.";
}
void pop()
{
char rmv;
if(top!=-1)
{
rmv=stk[top];
top--;
cout<<"\nElement removed was "<<rmv;
}
else
cout<<"\nThe stack is empty.";
}
void topele()
{
char t;
if(top!=-1)
t=stk[top];
else
{
t='#';
cout<<"\nThere are no elements in the stack.The stack is: "<<t;
}
}
int chkpres()
{
char ch;
switch(ch)
{
case '^': return 5;
break;
case '*': return 4;
break;
case '/': return 3;
break;
case '+': return 2;
break;
case '-': return 1;
break;
default: exit(1);
break;
}
}
int main()
{
char pre,pres,ele,elem,chk,poppy;
cout<<"\nEnter how many elements you want to enter in the infix expression: ";
cin>>n;
for(int j=0;j<n;++j)
{
cout<<"\nEnter the characters of the infix expression one by one: ";
cin>>ifx[j];
}
for(int i=0;ifx[i]='\0';++i)
{
if(ifx[i]=='(')
{
exit(1);
}
stk[-1]='#';
pfx[0]='#';
if(ifx[i]=='^'||ifx[i]=='*'||ifx[i]=='/'||ifx=='+'||ifx[i]=='-')
{
if(stk[top]=='^'||stk[top]=='*'||stk[top]=='/'||stk[top]=='+'||stk[top]=='-')
{
pre=ifx[i];
pres=stk[top];
chk=chkpres();
if(pre>pres)
{
stk[top]=pre;
top++;
}
else if(pres>=pre)
pfx[i]=pres;
}
}
else if(ifx[i]=')')
{
while(stk[top]!='#')
{
poppy=stk[top];
pfx[i]=poppy;
}
}
}
cout<<"\nThe postfix expression is: ";
for(int i=0;pfx[i]!='\0';++i)
{
cout<<pfx[i];
}
return 0;
}

Please help me soon...

this is not urgent for us, please don't mark it as such.

1 members found this post helpful.

Should have been
Next time, please use CODE tags when posting code.

Also, look at the error messages yourself. It tells you the error was in a comparison on line 80. You could have found your typo faster yourself with a careful look at line 80, than by asking here.

I usually ignore the word "urgent" in a post or title. Others may ignore the whole post. Anyway, it doesn't help.

Unfortunately, some typos don't yield compile time errors. Run time errors are harder to track down.

What do you expect that to accomplish?

1 members found this post helpful.

The program is:

//Convert an infix expression to postfix expression...

#include<iostream>
#include<string>
#include<cstdlib>
using namespace std;
char ifx[50],pfx[50],stk[50];
int top=-1,n;
char push(char ch)
{
if(top!=n)
{
ch=stk[top];
top++;
return ch;
}
else
cout<<"\nThe stack is full.";
}
void pop()
{
char rmv;
if(top!=-1)
{
rmv=stk[top];
top--;
cout<<"\nElement removed was "<<rmv;
}
else
cout<<"\nThe stack is empty.";
}
char topele()
{
char t;
if(top==-1)
t='#';
else
t=stk[top];
return t;
}
int chkpres()
{
char ch;
switch(ch)
{
case '^': return 5;
break;
case '*': return 4;
break;
case '/': return 3;
break;
case '+': return 2;
break;
case '-': return 1;
break;
default: exit(1);
break;
}
}
int main()
{
char pre,pres,ele,elem,chk,popp,topp;
cout<<"\nEnter how many elements you want to enter in the infix expression: ";
cin>>n;
topp=stk[top];
cout<<"\nEnter the characters of the infix expression one by one: ";
for(int i=0;i<n;++i)
{
cin>>ifx[i];
//for(int i=0;ifx[i]='\0';++i)
//{
if(ifx[i]!='^' && ifx[i]!='*' && ifx[i]!='/' && ifx[i]!='+' && ifx[i]!='-')
pfx[i]=ifx[i];
else if(ele=='(')
{
ele=ifx[i];
push(ele);
top++;
}
else if(ifx[i]=='^'||ifx[i]=='*'||ifx[i]=='/'||ifx[i]=='+'||ifx[i]=='-')
{
if(topp=='^'||topp=='*'||topp=='/'||topp=='+'||topp=='-')
{
pre=ele;
pres=topp;
chk=chkpres();
if(pre>pres)
{
topp=pre;
top++;
}
else if(pres>=pre)
pfx[i]=pres;
}
}
else if(ele=')')
{
while(topp!='#')
{
popp=topp;
pfx[i]=popp;
}
}
// }
}
cout<<"\nThe postfix expression is: ";
for(int i=0;pfx[i]!='\0';++i)
{
cout<<pfx[i];
}
return 0;
}



OUTPUT is:



Enter how many elements you want to enter in the infix expression: 9

Enter the characters of the infix expression one by one: a
*
(
b
+
c
)
/
d

The postfix expression is: a

Could you please help me to fix the error...

0 members found this post helpful.

You seem to have ignored most of what I said in post #3.

You should examine your whole program for where you have still misused = as if it were a comparison operator.

Also take a careful look at what your push function does and how you use it. There appear to be at least three different bugs in that. With so many bugs, it is hard to estimate what you really intended, so hard to say exactly which specific places are the bugs.

I expect there is a lot more than that wrong. But without CODE tags and proper indenting, I have no interest in taking a closer look to tell you more than is obvious at first glance.

4 members found this post helpful.

For something with such urgency, you would think it would be worthwhile to at least post in code tags to speed up scrutiny of the code. Sheesh.
--- rod.

1 members found this post helpful.

char pre,pres,ele,elem,chk,popp,topp,str;
cout<<"\nEnter how many elements you want to enter in the infix expression: ";
cin>>n;
topp=stk[top];
cout<<"\nEnter the characters of the infix expression one by one: ";
for(int i=0;i<n;++i)
{
cin>>ifx[i];
//for(int i=0;ifx[i]='\0';++i)
//{
if(ifx[i]!='^' && ifx[i]!='*' && ifx[i]!='/' && ifx[i]!='+' && ifx[i]!='-')
pfx[i]=ifx[i];
else if(ele=='(')
{
ele=ifx[i];
push(ele);
top++;
}

when all else fails, use cout to output the variable values to see what's going on. if you insert the line
cout << ele << endl;
after your 2 commented lines, you will see that 'ele' is never assigned. also, good form dictates initializing variables after the declaration, not in the middle of code where it's difficult to understand.

i'm not going to help you with the logic (it's slightly convoluted), you need to learn that on your own through many examples, but cout a variable when in doubt. it's refer to as a trace variable.

Why not use
instead?