Code not fully generating a post fix expression - c

Question

I was hoping to get a bit of help, my program is supposed to take a prefix expression and generate the post fix in order. for example the expression 234*+ should generate 23+4
I am getting: Enter postfix expression: 234+
Infix expression: (3*)(2+)
I think I am on the right track just not sure what I did wrong, Thank you in advance
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#define MAX_SIZE 100
typedef struct stack {
char data[MAX_SIZE];
int top;
} Stack;
void push(Stack *s, char x) {
if (s->top == MAX_SIZE - 1) {
printf("Stack overflow\n");
return;
}
s->top++;
s->data[s->top] = x;
}
char pop(Stack *s) {
if (s->top == -1) {
printf("Stack underflow\n");
return '\0';
}
char x = s->data[s->top];
s->top--;
return x;
}
int isOperator(char x) {
switch (x) {
case '+':
case '-':
case '/':
case '*':
return 1;
}
return 0;
}
int main() {
char postfix[MAX_SIZE];
char infix[MAX_SIZE];
printf("Enter postfix expression: ");
scanf("%s", postfix);
Stack s;
s.top = -1;
int i = 0;
while (postfix[i] != '\0') {
if (isOperator(postfix[i])) {
char op1 = pop(&s);
char op2 = pop(&s);
char temp[5];
temp[0] = '(';
temp[1] = op2;
temp[2] = postfix[i];
temp[3] = ')';
temp[4] = '\0';
strcat(infix, temp);
push(&s, op1);
} else {
push(&s, postfix[i]);
}
i++;
}
printf("Infix expression: %s\n", infix);
return 0;
}
I have been trying with a simple expression as stated above but not too sure what is messed up