Infix to postfix conversion

void infixTopostfix(char infix[], char postfix[]){
 int i,j=0;
Stack* evaluator = initialize();
 for(i=0; infix[i] ; ++i){
    if(isdigit(infix[i])) {
            postfix[j++] = infix[i];}
    else {
            while(!isempty(evaluator) && precedence(infix[i]) <= precedence((char)top(evaluator)))
                {postfix[j++] = pop(evaluator);}
                 push(evaluator,(int)infix[i]);

        }
                    }
                postfix[j++] = '\0';
                printf("%s",postfix);
 }

#include<stdlib.h>
#include<stdio.h>
#define SIZE 100
typedef struct
{
    int top;
    int *items;
} Stack;
Stack* initialize()
{
    Stack *s=malloc(sizeof(Stack));
    s->top=0;
    s->items=(int*) malloc(SIZE*sizeof(int));
    return s;
}
int isfull(Stack *s)
{
    return s->top >= SIZE ?1:0 ;
}
int isempty(Stack *s)
{
    return s->top==0?1:0;
}

void push(Stack *s,int value)
{
    if(!isfull(s))
        s->items[s->top++]=value;
    else printf("stack is full");
}
int pop(Stack *s)
{
    if(!isempty(s))
        return s->items[--s->top];
    else printf("stack is empty");
    return 404;
}
int top(Stack* s){
if(isempty(s)) return 0;
return (s->items[s->top]);
}