how to solve infix expression

[12345678]

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define MAX 10

struct opndstack
{
int top;
double items[MAX];
};

struct optrstack
{
int top;
char items[MAX];
};

void pushopnd(struct opndstack *s,double val)
{
if(s->top==MAX-1)
{
printf(“nStack Overflow.”);
exit(1);
}
else
{s->items[++(s->top)]=val;
}
}

double popopnd(struct opndstack *s)
{
if(s->top==-1)
{
printf(“nStack Underflow.”);
exit(1);
}
else
{
return(s->items[(s->top)--]);
}
}

void pushoptr(struct optrstack *s,char ch)
{
if(s->top==MAX-1)
{
printf(“nStack Overflow.”);
exit(1);
}
else
{s->items[++(s->top)]=ch;
}
}

char popoptr(struct optrstack *s)
{
if(s->top==-1)
{
printf(“nStack Underflow.”);
exit(1);
}
else
{
return(s->items[(s->top)--]);
}
}

int isdigit(char ch)
{return(ch>=’0′ && ch<=’9′);
}

int isoperator(char ch)
{
switch(ch)
{
case ‘+’:
case ‘-’:
case ‘*’:
case ‘/’:
case ‘^’:
return 1;
default:
return 0;
}
}

double eval(char ch,double opnd1,double opnd2)
{
switch(ch)
{
case ‘+’:return(opnd1+opnd2);
case ‘-’:return(opnd1-opnd2);
case ‘*’:return(opnd1*opnd2);
case ‘/’:return(opnd1/opnd2);
case ‘^’:return(pow(opnd1,opnd2));
default:printf(“nInvalid operator.”);
exit(1);
}
}

int precedence(char ch)
{
switch(ch)
{
case ‘#’: return 0;
case ‘+’:
case ‘-’: return 1;
case ‘*’:
case ‘/’:return 2;
case ‘^’:return 3;
case ‘(‘:return 4;
default :printf(“nInvalid operator.”);
exit(1);
}
}

double infix(char str[])
{
double opnd1,opnd2,value;
char ch;
opndstack opndstk;
optrstack optrstk;
opndstk.top=-1;
optrstk.top=-1;
pushoptr(&optrstk,’#');
int i=0;
char optr2;
for(i=0;str[i]!=’�’;i++)
{
if(isdigit(str[i]))
pushopnd(&opndstk,(double)(str[i]-’0′));
else if(isoperator(str[i]))
{optr2=popoptr(&optrstk);
if(precedence(str[i])>precedence(optr2))
{pushoptr(&optrstk,optr2);
pushoptr(&optrstk,str[i]);
}
else
{
while(precedence(str[i])<=precedence(optr2))
{ opnd2=popopnd(&opndstk);
opnd1=popopnd(&opndstk);
value = eval(optr2,opnd1,opnd2);
pushopnd(&opndstk,value);
optr2=popoptr(&optrstk);
}
pushoptr(&optrstk,optr2);
pushoptr(&optrstk,str[i]);
}
}
}
while((ch=popoptr(&optrstk))!=’#')
{
opnd2=popopnd(&opndstk);
opnd1=popopnd(&opndstk);
value=eval(ch,opnd1,opnd2);
pushopnd(&opndstk,value);
}
return(popopnd(&opndstk));
}

int main() {
char str[80];
int i;
printf(“nEnter an infix string?”);
for(i=0;(str[i]=getchar())!=’n';i++)
str[i]=’�’;
printf(“nInfix String = %s”,str);
printf(“nEvaluation of infix = %f”,infix(str));
return 0;
}

[weaknessforcats]

Exactly what help do you need?

I see a ton of code with no comments. Are you expecting me to debug this program?

[donbock]

1. Please enclose your code in CODE tags. That will make it easier to read and it provides line numbers. By the way, fix the spacing & indentation after you add the CODE tags.
2. Cut & paste your compilation error into your post so we don't have to guess what went wrong.
3. Typically, the line numbers in your source file don't match the line numbers in the snippet you post. Tell us which line of the snippet corresponds to the line number provided by the compiler error.

[donbock]

One thing that jumped out at me is a line near the bottom of your snippet:

str[i] = ' ';

Where the character between the single quotes is a square. I doubt that's a legal character constant in C.