逆波兰表达式求值

struct Stack
{
    int data;
    struct Stack* next;
};

void push(struct Stack* stack,int item)
{
    struct Stack* tem1 = (struct Stack*)malloc(sizeof(struct Stack));
    tem1->data = item;
    tem1->next = stack->next;
	stack->next = tem1;
}

int pop(struct Stack* stack)
{
    struct Stack* tem2 = (struct Stack*)malloc(sizeof(struct Stack));
	int p;
    tem2 =stack->next;
	p = tem2->data;
	stack->next = tem2->next;
	free(tem2);
    return p;
}

int evalRPN(char ** tokens, int tokensSize)
{
    struct Stack* stack = (struct Stack*)malloc(sizeof(struct Stack));
	stack->next = NULL;

    for(int i=0;i<tokensSize;i++)
    {
        if(tokens[i][0]==42)
        {
            int m = pop(stack)*pop(stack);
            push(stack,m);
        }
        else if(tokens[i][0]==43) 
        {
            int m = pop(stack)+pop(stack);
            push(stack,m);
        }
        else if((tokens[i][0]==45)&&(tokens[i][1]=='\0'))
        {
            int j = pop(stack);
            int m = pop(stack)-j;
            push(stack,m);
        }
        else if(tokens[i][0]==47)
        {
            int m = pop(stack)/pop(stack);
            push(stack,m);
        }
        else
        {
            int n = atoi(tokens[i]);
            push(stack,n);
        }
    }
    return pop(stack);
}