警告：赋值从整数中生成没有强制转换的指针[默认启用]

Question

我正在为家庭作业编写解析器，我收到以下警告：

parser.y:145:23: warning: assignment makes pointer from integer without a cast [enabled by default]
       $$ = manage_expr_arithop_expr($1, $3, add);

解析器的行是：

$$ = manage_expr_arithop_expr($1, $3, add);

和函数manage_expr_arithop_expr：

expr* manage_expr_arithop_expr(expr* expr1, expr* expr2, iopcode io_op)
{
    expr* expr;

    if(expr1 == NULL)
    {
        printf("Warning: expression1 op expression2, expression1 is NULL \n");
    }
    else if(expr2 == NULL)
    {
        printf("Warning: expression1 op expression2, expression2 is NULL \n");
    }
    if(expr1->type != constnum_e)
    {
        printf( "Warning: expression1 op expression2, expression1 is not a number");
    }
    else if(expr2->type != constnum_e)
    {
        printf("Warning: expression1 op expression2, expression2 is not a number\n");
    }

    expr = newexpr(arithexpr_e);
    expr->sym = new_temporary_variable();   
    printf("\n\nIn manage arithmetic expression  %p \n\n", expr);
    emit(io_op, expr, expr1, expr2, 0, yylineno);
    return  expr;
}

我该怎么办？