C PROGRAM TO CONVERT INFIX EXP INTO POSTFIX

#include<stdio.h>

#include<ctype.h>

#include<string.h>

main()

{

char infix[20],postfix[20],stack[20],ch,c;

int top=-1,i=0,j=0;

int preced(char);

clrscr();

printf("enter a valid infix expression\n");

gets(infix);

stack[++top]='#';

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

{

if(isalnum(ch))

postfix[j++]=ch;

else

{

switch(ch)

{

case '(':stack[++top]=ch;

break;

case ')':while((c=stack[top--])!='(')

postfix[j++]=c;

break;

default:while(preced(ch)<=preced(c=stack[top]))

{

postfix[j++]=c;

top--;

}

      stack[++top]=ch;

      }

    }

  }

while(top>0)

postfix[j++]=stack[top--];

postfix[j]='\0';

printf("\nresultant postfix expression:-%s",postfix);

getch();

}

int preced(char ch)

{

if(ch=='#'||ch=='(')

return(0);

else if(ch=='+'||ch=='-')

return(1);

else if(ch=='*'||ch=='/'||ch=='%')

return(2);

else if(ch=='^'||ch=='$')

return(3);

}