program to convert an expression from infix to postfix.

 Program is:

#include<iostream.h>

#include<conio.h>

#include<string.h>

#include<ctype.h>

const int MAX=50;

class infix

{

private:

char target[MAX],stack[MAX];

char *s,*t;

int top;

public:

infix();

void setexpr(char *str);

void push(char c);

char pop();

void convert();

int priority(char c);

void show();

};

infix::infix()

{

top=-1;

strcpy(target,"");

strcpy(stack,"");

t=target;

s="";

}

void infix:: setexpr(char *str)

{

s=str;

}

void infix::push(char c)

{

if(top==MAX)

cout<<"\n Stack is full\n";

else

{

top++;

stack[top]=c;

}

}

char infix::pop()

{

if(top==-1)

{

cout<<"\n Stack is empty\n";

return-1;

}

else

{

char item=stack[top];

top--;

return item;

}

}

void infix::convert()

{

while(*s)

{

if(*s==' '||*s=='\t')

{

s++;

continue;

}

if(isdigit(*s)||isalpha(*s))

{

while(isdigit(*s)||isalpha(*s))

{

*t=*s;

s++;

t++;

}

}

if(*s=='(')

{

push(*s);

s++;

}

char opr;

if(*s=='*'||*s=='+'||*s=='/'||*s=='%'||*s=='-'||*s=='$')

{

if(top!=-1)

{

opr=pop();

while(priority(opr)>=priority(*s))

{

*t=opr;

t++;

opr=pop();

}

push(opr);

push(*s);

}

else

push(*s);

s++;

}

if(*s==')')

{

opr=pop();

while((opr)!='(')

{

*t=opr;

t++;

opr=pop();

}

s++;

}

}

while(top!=-1)

{

char opr=pop();

*t=opr;

t++;

}

*t='\0';

}

int infix::priority(char c)

{

if(c=='$')

return 3;

if(c=='*'||c=='/'||c=='%')

return 2;

else

{

if(c=='+'||c=='-')

return 1;

else

return 0;

}

}

void infix::show()

{

cout<<target;

}

void main()

{

char expr[MAX];

infix q;

clrscr();

cout<<"\n Enter an expression in infix form:";

cin.getline(expr,MAX);

q.setexpr (expr);

q.convert();

cout<<"\n The postfix expression is:";

q.show();

getch();

}

output is: