Function peek

Stack/stack_implementation_using_array.c:44–51

    return x;
}
int peek(struct Stack st, int index)
{
    int x = -1;
    if (st.top - index + 1 < 0)
        printf("Invalid Index \n");
    x = st.S[st.top - index + 1];
    return x;
}
int isEmpty(struct Stack st)
{
    if (st.top == -1)