Infix To Prefix Conversion Using Stack :)

Following Code Converts  An Infix Expression To Prefix Expression :

#include<stdio.h>
#include<ctype.h>    //for isalnum function
#include<string.h>
char stack[50];
int top=-1;
void push(char x)
{
if(top==49)
{printf("Overflow");
}
else{

stack[++top]=x;
}
}
char pop()
{ if(top==-1)
{
return -1;
}
else{

return stack[top--];
}
}
int priority(char x)
{
if(x==')')
{ return 0;
}
else if(x=='+'||x=='-')
 return 1;
 else if(x=='*'||x=='/')
 return 2;
}
main()
{
char infix[50],pre[50];
char x,*e;
int i=0;
printf("Enter The Expression  ");
scanf("%s",infix);
strrev(infix);    //reversing the infix expression
e=infix;
while(*e!='\0')
{
if(*e==')')
{
push(*e);
}
else if(isalnum(*e))
{
pre[i++]=*e;
}
else if(*e=='(')
{
while((x=pop())!=')')
pre[i++]=x;
}
else
{
while(priority(stack[top])>=priority(*e))
pre[i++]=pop();
push(*e);
}
e++;
    }   while(top!=-1)
        pre[i++]=pop();
strrev(pre);      //reversing the result from procedure
                printf("Prefix Expression ");
printf("%s",pre);
}

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Output: