InfixToPostfix.c

/*Infix to postfix expression conversion*/

#include<stdlib.h>
#include<ctype.h>
#include<string.h>
#define MAX 100

char st[MAX];
int top=-1;

void push(char st[],char);
char pop(char st[]);
void InfixtoPostfix(char source[],char target[]);
int getPriority(char);

int main()
{
char infix[100],postfix[100];
printf(“\n Enter any Infix Expression: ”);
scanf(“%s”,infix);
strcpy(postfix,””);
InfixtoPostfix(infix,postfix);
printf(“\n The corresponding postfix Expression is: ”);
puts(postfix);
return 0;
}

void InfixtoPostfix(char source[],char target[])
{
int i=0,j=0;
char temp;
strcpy(target,””);
while(source[i]!=’\0’)
{
 if(source[i]==’(‘)
 {
 push(st,source[i]);
 i++;
}

else if(source[i]==’)’)
{
 while((top!=-1)&&(st[top]!=’(‘))
 {
  target[j]=pop(st);
  j++;
 }
 if(top==-1)
 {
  printf(“\n  incorrect Expression”);
return;
}
temp=pop(st);
i++;
}

else if(isdigit (source[i]) || isalpha(source[i]))
{
target[j]=source[i];
j++;
i++;
}

else if(source[i]==’+’ || source[i]==’_’ || source[i]==’*’ || source[i]==’/’ || source[i]==’%’)
{
while((top!=-1)&&(st[top]!=’(‘)&&(getpriority(st[top])>getpriority(source[i])))
{
target[j]=pop(st);
j++;
}
push(st,source[i]);
i++;
}

else
{
printf(“\n incorrect element in expression”);
return;
}
}

while((top!=-1)&&(st[top]!=’(’))
{
target[j]=pop(st);
j++;
}
target[j]=’\0’;
}

int getPriority(char op)
{
 if(op==’/’||op==’*’||op==’%’)
return 1;
else if(op==’+’||op==’%’)
return 0;
}

void push(char st[],char val)
{
if(top==MAX-1)
printf(“\n stack overflow”);
else
{
top++;
st[top]=val;
}
}

char pop(char st[])
{
char val=’ ’;
if(top==-1)
printf(“\n stack underflow”);

else
{
val=st[top];
top--;
}
return val;
}