C program to perform infix to postfix conversion.

#include<stdio.h>

#include<conio.h>

#include<string.h>

#include<ctype.h>

#define MAX 100

char s[MAX];

int top=-1;

push(char elem)

{

s[++top]=elem;

return top;

}

char pop()

{

return(s[top--]);

}

int pr(char elem)

{

switch(elem)

{

case '#': return 0;

case '(': return 1;

case '+':

case '-': return 2;

case '*':

case '/': return 3;

}

return elem;

}

void main()

{

char infix[50],postfix[50],ch,elem;

int i=0,k=0;

clrscr();

printf("enter infix expression\n");

scanf("%s",infix);

push('#');

while((ch=infix[i++])!='\0')

{

if(ch=='c')

push(ch);

else if(isalnum(ch))

postfix[k++]=ch;

else if(ch==')')

{

while(s[top]!='(')

postfix[k++]=pop();

elem=pop();

}

else

{

while(pr(s[top])>=pr(ch))

postfix[k++]=pop();

push(ch);

}

}

while(s[top]!='#')

postfix[k++]=pop();

postfix[k]='\0';

printf("postfix expression is: %s\n",postfix);

getch();
}

output: